全文获取类型
收费全文 | 22270篇 |
免费 | 278篇 |
国内免费 | 1篇 |
专业分类
林业 | 4014篇 |
农学 | 1413篇 |
基础科学 | 183篇 |
3732篇 | |
综合类 | 1844篇 |
农作物 | 2419篇 |
水产渔业 | 2153篇 |
畜牧兽医 | 3190篇 |
园艺 | 1282篇 |
植物保护 | 2319篇 |
出版年
2023年 | 34篇 |
2022年 | 33篇 |
2021年 | 118篇 |
2020年 | 118篇 |
2019年 | 127篇 |
2018年 | 2814篇 |
2017年 | 2770篇 |
2016年 | 1284篇 |
2015年 | 171篇 |
2014年 | 157篇 |
2013年 | 271篇 |
2012年 | 1105篇 |
2011年 | 2485篇 |
2010年 | 2280篇 |
2009年 | 1403篇 |
2008年 | 1691篇 |
2007年 | 1951篇 |
2006年 | 424篇 |
2005年 | 497篇 |
2004年 | 513篇 |
2003年 | 548篇 |
2002年 | 420篇 |
2001年 | 81篇 |
2000年 | 100篇 |
1999年 | 67篇 |
1998年 | 49篇 |
1997年 | 39篇 |
1996年 | 68篇 |
1995年 | 54篇 |
1994年 | 48篇 |
1993年 | 62篇 |
1992年 | 59篇 |
1991年 | 32篇 |
1990年 | 50篇 |
1989年 | 47篇 |
1988年 | 44篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 33篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Jiwan P Palta 《Potato Research》2010,53(4):267-275
Calcium plays a major role in plant growth and development and in the maintenance and modulation of various cell functions,
especially related to membrane structure and function and to cell wall structure. Calcium stabilizes cell membranes by bridging
polar head groups of phospholipids at the membrane surface. Calcium is also an integral part of the cell wall where it provides
stable intra-molecular linkages between pectin molecules, resulting in cell wall rigidity. A change in the cytosolic calcium
concentration is also known to provide a cellular signal that regulates metabolism and mediates plant responses to stresses. 相似文献
992.
Kimihiko Hyakumura 《Small-Scale Forestry》2010,9(3):349-367
A progressive part of protected area management program in Lao PDR is a land and forest allocation program which contains
critical elements that delegate right of land and forest use to local people. This study analyzes the gap between the original
intent of the program and its actual implementation by local officials in Phou Xang He protected area, and discusses policy
issues that need to be addressed. It appears that several types of non-compliance with regulations by local people have occurred,
with local officials tacitly ignoring infractions. By switching viewpoints, however, it appears that the local officials permit
these infractions as a way of allowing local people to secure their livelihoods. As constraints on the realities of land and
forest use vary widely in and around villages in different locales, there is a need for government to allow local officials
flexibility in implementing policies. 相似文献
993.
The formation of dental calculus in dogs is a major problem. Scanning electron microscopy of tartar specimens from dogs revealed on the outer surface of the plaque polymorphic configurations, more or less arranged as free filaments, corn-cobs or swab-like structures. Uninhabited bacterial recesses were found on the inner surface of the calculus. Calcification may occur between or within the bacteria. Elucidating the mechanisms of calculus formation should help in the development of prophylactic measures. 相似文献
994.
995.
996.
Peter D. Constable BSc Phd Robert N. Streeter Gerard J. Koenig Nigel R. Perkins Hani M. Gohar Dawn E. Morin 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1997,11(2):71-79
The objectives of this study were to investigate the determinants of the anion gap (AG) in cattle and to evaluate the utility of AG in detecting hyperlactatemia in sick neonatal calves and adult cattle. The AG was calculated as AG = ([Na+] + [K+]) - ([Cl-] + [HCO3]), with all values in mEq/L. The AG of healthy neonatal calves (n = 16) was 29.6 ± 6.2 mEq/L (mean ± SD), and the blood L-lactate concentration ranged from 0.5 to 1.2 mM/L. The AG was significantly (P > .05) correlated with serum phosphate (r = .66) and creatinine (r = .51) concentrations. The AG of neonatal calves with experimentally induced diarrhea (n = 16) was 28.6 ± 5.6 mEq/L, and the blood L-lactate concentration ranged from 1.1 to 2.9 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .67), serum phosphate concentration (r = .63), creatinine concentration (r = .76), and blood pH (r = -.61). The AG of adult cattle with abomasal volvulus (n = 41) was 20.5 ± 7.8 mEq/L, and the blood L-lactate concentration ranged from 0.6 to 15.6 mM/L. The AG was significantly correlated with blood L-lactate concentration (r = .60), serum phosphate concentration (r = .71), creatinine concentration (r = .65), albumin concentration (r = .47), total protein concentration (r = .54), blood pyruvate concentration (r = .67), and blood pH (r = -.41) but not plasma β-OH butyrate concentration. The results indicate that the AG in cattle is only moderately correlated with blood L-lactate concentration and is similarly correlated with serum phosphate and creatinine concentrations in neonatal calves and adult cattle, as well as with serum albumin and total protein concentrations in adult cattle. Anion gap determination is of limited usefulness in predicting blood L-lactate concentration in sick cattle, whereas the correlation between AG and serum creatinine concentration in sick cattle suggests that an increased AG should alert the clinician to the potential presence of uremic anions. 相似文献
997.
John T. Hathcock DVM MS D. G. Pugh DVM MS Robert E. Cartee DVM MS Linda Hammond DVM 《Veterinary radiology & ultrasound》1995,36(4):290-296
Computed tomography was performed on the head of 6 normal adult llamas. The animals were under general anesthesia and positioned in dorsal recumbency on the scanning table. The area scanned was from the external occipital protuberance to the rostral portion of the nasal passage, and the images are presented in both a bone window and a soft tissue window to allow evaluation and identification of the anatomy of the head. Computed tomography of the llama head can be accomplished by most computed tomography scanners utilizing a technique similar to that used in small animals with minor modification of the scanning table. 相似文献
998.
Robert N. White BSc BVetMed Nicholas J. Macdonald BVetMed Carolyn A. Burton BVetMed PHD 《Veterinary radiology & ultrasound》2003,44(5):514-521
A retrospective study of the use of intraoperative mesenteric portovenography (IOMP) in the surgical management of congenital portosystemic shunts in 100 dogs and cats was performed. Each portovenogram was scored using a subjective visual analogue scale (VAS) and was assessed for the presence of portal atresia or hypoplasia. VAS scores and portal hypoplasia assessments were obtained for portovenogram images obtained for each animal both before shunt manipulation (preligation) and following the temporary, complete ligation of the vessel (postligation). In each patient, surgical records were reviewed to ascertain the degree of shunt attenuation that was achieved at surgery. Hepatic portal vasculature was significantly different on postligation compared with preligation IOMP. Sixty-two percent of animals had apparent portal hypoplasia or atresia on their preligation IOMP. The majority of these (81%) had an improvement in portal vasculature on postligation IOMP. It was concluded that both preligation and postligation IOMP provided valuable information regarding the morphology of congenital portosystemic shunts. An accurate assessment of an animal's portal vasculature could only be made following the interpretation of a postligation portovenogram, and these findings significantly influenced the surgical management of the patient. Although individuals with high postligation VAS scores were more likely to achieve full shunt attenuation at surgery, there was no quantifiable relationship between IOMP findings and the degree of shunt attenuation achieved. 相似文献
999.
1000.