首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2464篇
  免费   234篇
林业   5篇
农学   2篇
基础科学   4篇
  8篇
综合类   12篇
农作物   2篇
水产渔业   21篇
畜牧兽医   2638篇
园艺   2篇
植物保护   4篇
  2024年   1篇
  2023年   53篇
  2022年   1篇
  2021年   3篇
  2020年   96篇
  2019年   4篇
  2018年   60篇
  2017年   67篇
  2016年   41篇
  2015年   69篇
  2014年   106篇
  2013年   110篇
  2012年   71篇
  2011年   85篇
  2010年   81篇
  2009年   86篇
  2008年   66篇
  2007年   54篇
  2006年   35篇
  2005年   28篇
  2004年   58篇
  2003年   56篇
  2002年   66篇
  2001年   64篇
  2000年   56篇
  1999年   68篇
  1998年   104篇
  1997年   101篇
  1996年   80篇
  1995年   79篇
  1994年   71篇
  1993年   90篇
  1992年   106篇
  1991年   80篇
  1990年   92篇
  1989年   76篇
  1988年   70篇
  1987年   76篇
  1986年   34篇
  1985年   48篇
  1984年   34篇
  1983年   48篇
  1982年   18篇
  1981年   1篇
  1980年   2篇
  1977年   1篇
  1976年   1篇
  1968年   1篇
排序方式: 共有2698条查询结果,搜索用时 15 毫秒
111.
Objective —To describe function and identify factors that affect outcome in dogs undergoing limb salvage surgery for osteosarcoma (OS) of the proximal humerus.
Study Design —A retrospective study of dogs in which OS of the proximal humerus was treated with limb salvage surgery.
Animals —17 client-owned dogs.
Methods: Records were analyzed for functional outcome, recurrence, metastasis, and survival.
Results —Outcome was good to excellent in 12% of dogs. Recurrence, metastasis, and survival were significantly affected by completeness of surgical margins. Double plating of the distal allograft-host junction significantly reduced frequency of biomechanical failure.
Conclusions —Limb salvage surgery for OS of the proximal humerus did not result in acceptable function and was fraught with postoperative complications. Outcome was significantly affected by completeness of surgical margins.
Clinical Relevance —Limb salvage surgery for OS of the proximal humerus in dogs cannot be recommended until improvement in functional outcome and reduction in postoperative complications can be achieved. The dependence of outcome on completeness of surgical margins supports aggressive en bloc resection and marking and evaluating surgical margins.  相似文献   
112.
Objective —To compare the insertional characteristics of external fixator pins with hollow ground (HG), modified HG, and trocar (T) points.
Study Design —An acute, in vitro biomechanical evaluation.
Sample Population—Thirteen radii from canine cadavers.
Methods —A total of 16 T-tipped and 16 HG-tipped pins were inserted into 8 canine radii. Ten pins of each modification of the HG tip (length of the cutting edge reduced by 0.127 mm and 0.254 mm, respectively) were inserted into another five radii. All pins were inserted with low-speed power drilling and 80 N drilling load. Differences between peak tip temperature, drilling energy, and pullout force were determined for each pin type at both diaphyseal and metaphyseal locations.
Results —HG-tipped pins showed a 40% lower tip temperature in diaphyseal bone, a 25% reduction in drilling energy in diaphyseal bone, and a reduction of pullout force in both diaphyseal (65%) and metaphyseal (50%) bone compared with T-tipped pins. HG 0.254-mm pins generated higher tip temperatures and had greater pullout than HG pins in diaphyseal bone.
Conclusions —The HG tip was a more efficient design; however, the reduction in pullout force suggests that, because a better hole was drilled, radial preload is reduced. Reduction of the cutting edge by 0.254 mm increased the pullout force but also increased the temperatures.
Clinical Relevance —Thermal and microstructural damage are reduced by the HG tip, but pin-bone interface stability is also compromised. The use of a tip with 0.254 mm reduction in the cutting edge may optimize the biological and mechanical factors at the pin-bone interface.  相似文献   
113.
Objective—To assess feasibility of insertion of 4.5-mm Herbert cannulated bone screws (HS) using fluoroscopic guidance and compare the mechanical shear strength of these HS and 4.5-mm AO cortical bone screws (AO) for fixation of dorsal plane slab osteotomies in equine cadaver third carpal bones (C3).
Animals or Sample Population—Eight equine cadavers.
Methods—Bone mineral composition and density of contralateral C3 were confirmed to be equivalent using dual-energy x-ray absorptiometry. A standard 10-mm C3 slab osteotomy was reduced using HS or AO instrumentation under fluoroscopic guidance. Specimens were loaded in shear until failure, using a materials testing apparatus.
Results—HS and AO instrumentation allowed accurate reconstruction of the osteotomy, but there was difficulty encountered seating the HS proximal self-tapping threads. There was no significant difference in maximal load to failure, stiffness, or mode of failure of constructs created with the HS and AO screws.
Conclusions —Use of 4.5-mm HS for repair of C3 radial facet, dorsal plane slab fractures may result in a mechanically comparable fixation to a repair using a 4.5-mm AO. Equine dorsal C3 may be too dense, however, to allow placement of the proximal self-tapping threads of the HS without potentially excessive application of torque to the screw itself.
Clinical Relevance —Dorsal plane, radial facet slab fractures of the equine C3 are a significant clinical problem. Accurate reconstruction and stabilization are necessary for return to athletic function.  相似文献   
114.
Objective —To determine if omentectomy would decrease the frequency of postoperative intraabdominal adhesions. Study Design —Retrospective study. Animals or Sample Population—44 horses that had either two ventral median celiotomies or a ventral median celiotomy and a necropsy more than 4 days later; 19 of these horses had their omentum removed at the initial surgery. Methods —Data retrieved from the records included location and type of intraabdominal adhesions; location of the surgical lesion; relationship of adhesions to the surgical lesion; surgical procedures; duration of initial surgery; time interval between procedures; age, gender, and breed of the horse; and clinical outcome. Fisher's exact test was used to evaluate the association between categorical explanatory and outcome variables. The effect of potential risk factors on the incidence rate of adhesion formation was estimated using a proportional hazards regression model. Results —Of 25 horses in the nonomentectomy group, 15 (60%) had postoperative adhesions that resulted in the need for a second surgical intervention, whereas of 19 horses that had omentectomy initially, only 4 (21%) had postoperative adhesions that required a second procedure. Rate of adhesion formation was higher in horses that did not have omentectomy initially (incidence ratio rate [IRR], 0.46; 90% confidence interval [CI], 0.18 to 1.19). At initial surgery, 24 horses had a small intestinal lesion, and 20 horses had a large intestinal lesion. Fifteen horses (63%) with small intestinal lesions subsequently developed adhesions compared with four horses (20%) with an initial large intestinal lesion (P= .006). At the second procedure, small intestine lesions were identified in 32 horses and large intestine lesions in 12 horses (1 horse had both small and large intestine lesions), and 1 horse had a gastric lesion. Adhesions were identified as the cause of colic signs in 19 (61%) horses with small intestinal lesions and in none of the horses with large intestine lesions. The frequency of adhesion development leading to colic associated with only the small intestine at the second surgery or necropsy was significantly greater (P= .001) than the frequency only in the large intestine. Conclusions —Omentectomy reduced the rate of postoperative adhesion formation. Adhesions are more likely to occur after small intestinal surgery and if they do occur likely involve the small intestine. Clinical Relevance —Omentectomy is a safe procedure and should be considered prophylactically for reduction of adhesion formation after abdominal surgery in horses.  相似文献   
115.
Brucellosis in sheep, caused by Brucella ovis, is primarily a chronic infectious disease of rams with epididymitis as its most characteristic lesion. Six hundred rams from an infected farm were clinically and serologically examined once a year, over a 3-year period. An increase from 2.1% to 6.3% in the prevalence of animals serologically positive to B. ovis occurred over the 3 years. However, the prevalence of rams with lesions in the reproductive tract declined from 14.2% to 6.5% in the third year following one year of strict culling of clinically affected and rams that were serologically positive for B. ovis. Clinical lesions found in the 179 affected rams fell into two main categories: rams with epididymitis and rams with affected lymph nodes. These results suggest that the prevalence of the disease relates mainly to the sexual activity of the animal and not to age in itself. A single cull based on the results of clinical examination and serological test results was unable to decrease the prevalence of B. ovis in an extensive Corriedale sheep flock.  相似文献   
116.
THE DURAL TAIL SIGN IN THE DIAGNOSIS OF MENINGIOMAS   总被引:3,自引:0,他引:3  
John P.  Graham  MVB  MSc  Susan M.  Newell  DVM  MS  Andra K.  Voges  DVM  Gregory D.  Roberts  DVM  MS  Jay M.  Harrison  MS 《Veterinary radiology & ultrasound》1998,39(4):297-302
In humans the dural tail is a sign seen on contrast enhanced T1 weighted magnetic resonance images. This finding is considered specific for meningioma. The purpose of this study was to determine how often the dural tail occurs in cats and dogs and whether it is a specific sign for meningiomas in these species. MR examinations for eighteen dogs and four cats with proven diagnoses were reviewed. Diagnoses included ten meningiomas (seven dogs and three cats), three gliomas, two pituitary tumors, single examples of two other tumor types and five patients with mass lesions due to inflammatory disease. Contrast enhanced T1 weighted images were evaluated independently by three of the authors for the presence of a dural tail, without knowledge of the diagnoses. The results were compared to the diagnosis for each patient and the performance of individual reviewers compared. When their results were averaged, the reviewers reported the presence of a dural tail in 6 of 10 (60%) meningiomas, although detection varied between observers from 40% to 80%. Each reviewer had one false positive result, two reported a dural tail with a chromophobe adenocarcinoma and one with a toxoplasma meningoencephalitis. When a dural tail is seen an associated mass is most likely a meningioma. It is uncertain whether the dural tail represents neoplastic infiltration beyond the margins of the meningioma. This should be considered when planning treatment.  相似文献   
117.
Image magnification is inherent in radiography. In digital fluoroscopy, the three components of magnification are geometric, electronic and photographic. In this study, the total magnification factor of a digital imaging system was determined by two methods, 1) comparison of measurements of a known object to its image and 2) calculation of geometric, electronic and photographic magnification from the imaging system specifications. Both methods were employed for various focal-film distances, image intensifier tube modes and laser printer formats. Results of these two methods were different due to the detrimental effect of penumbra on image quality with increasing magnification. If a radiographic image is to be used to approximate object size, then a technique should be used that will minimize magnification. In digital fluoroscopy this is achieved with the shortest object-film distance (assuming a fixed focal-object distance), largest image intensifler mode and greatest number of images per sheet of film.  相似文献   
118.
FACIAL FIBROSARCOMA IN TWO COWS   总被引:1,自引:0,他引:1  
Fibrosarcoma is a common tumor affecting bone, but is uncommon in cows, Reported here are two bovine cases of facial fibrosarcoma that were very invasive.  相似文献   
119.
Tracy  Ladue  DVM  G. Sylvester  Price  DVM  PhD  Richard  Dodge  MS  Rodney L.  Page  DVM  MS  Donald E.  Thrall  DVM  PhD 《Veterinary radiology & ultrasound》1998,39(1):57-62
The records of 56 dogs treated with megavoltage radiation for mast cell neoplasia were reviewed to determine the efficacy of this treatment modality. Total radiation dose ranged from 45 to 57 Gray (Gy), dose per fraction ranged from 3.0 to 4.0 Gy, and radiation treatment time ranged from 14–28 days. Median disease free interval (95% CI) was 32.7 (19–70) months. Median disease free interval for dogs older than 7.5 years was 15 (lower limit 7) months as compared to 62 (lower limit 20) for dogs younger than 7.5 years of age (p = 0.006). Median disease free interval for dogs with measurable disease was 12 (lower limit 5) months as compared to 54 (32–70) months for dogs with microscopic disease (p = 0.006). Radiation treatment time was also significantly related to disease free interval. Median disease free interval for dogs treated longer than 22 days was 12 (7–19) months as compared to greater than 50 (lower limit 20) months for dogs treated in 22 or fewer days (p < 0.001). This appeared to be due to more recurrences in dogs treated with 3-per-week fractionation and suggests that tumor proliferation in the interfraction interval may be important. Sex, tumor location, histologic grade, WHO clinical stage, number of radiation fractions, total radiation dose, and dose-per-fraction, as well as the following "yes/no" variables: steroids given, surgery prior to radiation, lymph nodes irradiated, and development of another mast cell tumor did not appear to influence median disease free interval or survival. Data presented herein support megavoltage radiation as an effective treatment for canine mast cell neoplasia, and suggest that disease free interval in dogs treated with daily fractions may be longer than that achieved with alternating day fractions.  相似文献   
120.
Debra K.  Baird  DVM  John T.  Hathcock  DVM  MS  Steven A.  Kincaid  DVM  MS  PhD  Paul F.  Rumph  DVM  MS  John  Kammermann  MS  William R.  Widmer  DVM  MS  Denise  Visco  PhD  Donald  Sweet  MD 《Veterinary radiology & ultrasound》1998,39(3):167-173
Six healthy adult male mongrel dogs underwent cranial cruciate ligament transection in the left stifle. Survey radiography of both stifles and low-field (0.064 T) MRI of the left stifle were performed preoperatively and at 2, 6, and 12 weeks postoperatively. Focal changes in signal intensity were seen with MRI in the subchondral bone of the medial tibial condyle at 2 and 6 weeks postoperatively. At 12 weeks postoperative, a cyst-like lesion was detected using MRI in the subchondral bone of the medial tibial condyle in 4 of 6 dogs and a less defined lesion at this site in the remaining 2 dogs. The cyst-like lesion was spherical in shape and showed typical characteristics of fluid with low signal intensity on T1-weighted images, high signal intensity on T2-weighted images and high signal intensity on inversion recovery images. The lesion was seen in the subchondral bone of the caudal medial and/or middle region of the tibial plateau slightly cranial to the insertion of the caudal cruciate ligament. No subchondral cysts were seen in the tibia on radiographs. Histopathologically, the tibia was characterized by a loose myxomatous phase of early subchondral cyst formation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号