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   277552篇
  免费   16022篇
  国内免费   664篇
林业   24039篇
农学   14160篇
基础科学   2984篇
  44774篇
综合类   30320篇
农作物   17212篇
水产渔业   17510篇
畜牧兽医   112318篇
园艺   6351篇
植物保护   24570篇
  2020年   2910篇
  2019年   3708篇
  2018年   4257篇
  2017年   4691篇
  2016年   4989篇
  2015年   4470篇
  2014年   5813篇
  2013年   16375篇
  2012年   7159篇
  2011年   9265篇
  2010年   7774篇
  2009年   8265篇
  2008年   8612篇
  2007年   7712篇
  2006年   8129篇
  2005年   7264篇
  2004年   7101篇
  2003年   6898篇
  2002年   6207篇
  2001年   7276篇
  2000年   6931篇
  1999年   6256篇
  1998年   4255篇
  1997年   4314篇
  1996年   4026篇
  1995年   4630篇
  1994年   4028篇
  1993年   3722篇
  1992年   4892篇
  1991年   4993篇
  1990年   4738篇
  1989年   4720篇
  1988年   4109篇
  1987年   4226篇
  1986年   4115篇
  1985年   4387篇
  1984年   3982篇
  1983年   3688篇
  1982年   2993篇
  1981年   2908篇
  1980年   2839篇
  1979年   3423篇
  1978年   3112篇
  1977年   2779篇
  1976年   2654篇
  1975年   2619篇
  1974年   2856篇
  1973年   2751篇
  1972年   2526篇
  1971年   2516篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Genoa salami, proscuittini and proscuitto were prepared from pork carcasses that were heavily infected experimentally with Trichinella spiralis spiralis. Genoa salami was prepared with salt concentrations of 2.0%, 2.75% and 3.3%. Proscuitto was prepared by two procedures approved by Agriculture Canada. At various times postpreparation, samples of the various cured products were taken and examined by pepsin digestion and rat bioassay for the presence of viable trichinae. Water activity and pH of the cured meat were also determined. Curing of the various products was shown to destroy the Trichinella larvae. Pepsin digestion revealed that larvae progressively became loosely coiled, uncoiled and more subject to digestion (ghost larvae) during the curing process. Rat bioassay revealed the presence of viable trichinae in the proscuitto prepared using a sodium chloride salt mixture at day 34 but not at day 48 postpreparation. All other bioassays carried out on Genoa salami between 13 and 42 days postpreparation, on proscuittini between days 27 and 69 and on proscuitto between days 34 and 69 were negative for viable trichinae. Under the conditions of this study, preparing Genoa salami with salt concentrations as low as 2% did not appear to affect the destruction of Trichinella larvae.  相似文献   
993.
The purpose of this study was to characterize the pharmacokinetics of a subcutaneously implanted tissue-chamber model. Thermoplastic tissue chambers were implanted in the paralumbar fossae of six steers. Starting 30 days after implantation, the distribution of intravenously administered antipyrine and phenylbutazone into the tissue chambers was studied. These pharmacokinetic experiments were repeated 10 days later to determine the effect of time after implantation on tissue-chamber distribution. Fifty days after implantation, tissue chambers were drained of transudate, refilled with sterile saline and the rate of influx of endogenous urea, creatinine and albumin was measured. Delayed diffusion of antipyrine and phenylbutazone into tissue chambers was well described using a compartmental model in which tissue-chamber fluid represented the third of three compartments arranged in series. The distribution of antipyrine into tissue chambers was greater than that of phenylbutazone; an observation which is well correlated with the high degree of protein binding of phenylbutazone. There was no effect of time on the penetration of the two agents. Rapid diffusion of urea and creatinine and extremely slow influx of albumin into chambers showed that these chambers formed true interstitial compartments.  相似文献   
994.
Antagonism of medetomidine sedation by atipamezole in pigs.   总被引:1,自引:0,他引:1  
The efficacy of atipamezole as a medetomidine antagonist was evaluated in pigs. The atipamezole doses (intramuscularly) were 80, 160, 320 and 480 micrograms/kg of body weight, which were one, two, four and six times higher than the preceding medetomidine dose (80 micrograms/kg, intramuscularly). Atipamezole effectively reversed medetomidine-induced sedation, and the optimal action was seen at doses of 160 and 320 micrograms/kg. Recovery from sedation was quick and smooth, and adverse effects such as hyperactivity or tachycardia were minimal with either dose.  相似文献   
995.
A 2-year-old female Japanese domestic cat weighing 3.6 kg was presented due to marked abdominal distention and was diagnosed as hepatic cyst. The bile acid concentration of the hepatic cyst was as low as the serum bile acid concentration. The membrane of the cysts was excised from the edge of the compressed hepatic tissue and no other surgical manipulation was performed. This surgical procedure is simple and quick compared to hepatic lobectomy, however, it is necessary to evaluate the fluid of the cyst before performing this procedure.  相似文献   
996.
As in the number of mammals, the most prominent feature of the ganglion-cell layer in the retina of the German shepherd dog is the sharp increase in the density of ganglion cells in the central area. There is an area of maximum density and also a ‘cat-like’ visual streak, located dorsal to the optic disc. The isodensity lines of ganglion-cell distribution is roughly concentric. Their values vary from 5300-13 000 cells/mm2 in the central area, with the cells densely packed, to 1000 cells/mm2 or less in the periphery, where the cells are sparsely distributed. There were some individual differences amongst the animals studied, although all of them were pure-bred dogs. This suggests that the configuration of the retina in the canine species is not only dependent on the breed itself but also on some other parameters such as phylogenetic heritage, environment, aptitude, lifestyle, or even training.  相似文献   
997.
Résumé— Une analyse rétrospective clinicopathologique a été menée chez 100 chiens présentant une hydradénite suppurative diagnostiquée par biopsie cutanée. Aucune prédisposition d'âge, de race ou de sexe n'a été mise en évidence. Tous les chiens présentaient cliniquement une folliculite bactérienne, ou une furonculose, ou les deux, qu'elle soit primaire ou secondaire à d'autres dermatoses. Aucene lésion clinique n'était pathognomonique d'hidradénite suppurative. Chez 73 chiens, l'hidradénite suppurative était associée microscopiquement à des degrés variables d'inflammation du follicule pileux. Chez 27 chiens, l'hidradénite suppurative était la seule évidence histologique d'inflammation annexielle. L'observation histopathologique d'hidradénite suppurative suggère l'existence sur le plan clinique d'une folliculite bactérienne, d'une furonculose, ou des 2. [Scott, D.W. Suppurative inflammation of apocrine sweat glands (suppurative hidradentis) in the dog: a retrospective clinicopathological analysis of 100 cases (inflammation suppurative des glandes sudorales apocrines (hidradénite suppurative) chez le chien: une analyse rétrospective clinicopathologique de 100 cas). Resumen— Se llevó a cabo un estudio clinicopatológico retrospectivo en 100 perros con hidradenitis supurativa diagnosticada mediante biopsia cutánea. No se detectó predominancia alguna de raza, sexo o edad. A todes los perros se les habia diagnosticado clinicamente foliculitis o furunculosis bacteriana, o ambas, ya sea de forma primaria o secundaria a otras dermatosis. No se encontraron lesiones clinicas especificas indicativas de hidradenitis supurativa. En 73 animales, la hidradenitis supurativa estaba asociada con varios grados de inflamación folicular a nivel microscópico. En los 27 casos restantes, los anejos presentaban unicamente hidradenitis supurativa. La presencia de hidradenitis supurativa a nivel microscópico sugiere la existencia de foliculitis o furunculosis bacteriana clinicas, o de ambas. [Scott, D.W. Suppurative inflammation of apocrine sweat glands (suppurative hidradenitis) in the dog: a retrospective clinicopathological analysis of 100 cases (inflamación supurativa de las glándulas sudoriparas apocrinas (hidradenitis supurativa) en el perro: estudio clinicopatológico retrospectivo de 100 casos). Abstract— A retrospective clinicopathological study was conducted on 100 dogs with suppurative hidradenitis as determined by skin biopsy. No apparent age, breed, or sex predilections were recognized. All dogs had been given a clinical diagnosis of bacterial folliculitis, furunculosis, or both of these, whether primary or secondary to other dermatoses. There were no clinical lesions that uniquely suggested the presence of suppurative hidradenitis. In 73 dogs, suppurative hidradenitis occurred in conjunction with varying degrees of hair follicle inflammation microscopically. In 27 dogs, suppurative hidradenitis was the only histological evidence of adnexal inflammation. The histopathologic finding of suppurative hidradenitis suggests the existence of clinical bacterial folliculitis, furunculosis, or both of these.  相似文献   
998.
To determine whether prolactin has luteolytic properties during the first part of the luteal period, hysterectomy was performed in four dogs, in which prolactin had been chronically suppressed by bromocriptine administration. The concentration of progesterone in the peripheral blood decreased upon hysterectomy during the first part of the luteal phase and regained normal values after about seven days. The progesterone patterns during the perisurgical period in these dogs were similar to those patterns observed in dogs hysterectomised without bromocriptine treatment. It is concluded therefore that, in the dog, luteolytic properties can not be attributed to prolactin.  相似文献   
999.
Lymphocytes, monocytes, granulocytes, B-lymphocytes and CD8-positive T-lymphocytes of non-infected mink and mink infected with Aleutian disease virus (ADV) were measured by flow cytometry. The gammaglobulin levels of the sera were also measured. Besides development of hypergammaglobulinaemia in the infected mink, the most pronounced finding was that the number of CD8-positive lymphocytes doubled on average during development of Aleutian disease, while the number of B-lymphocytes did not change dramatically. The enhanced CD8 frequency was still apparent 6 months after initial ADV infection of the mink. The present experiments contribute to a better understanding of the immune deficiency stage seen in mink infected with ADV.  相似文献   
1000.
A three-phase laboratory procedure suitable for predicting protein degradability in the rumen and digestibility of undegraded protein is reported. In the first phase the feed was incubated with starch and buffered rumen fluid. In the incubation mixture the viability of protease-active bacteria was checked by anaerobic culturing, whereas changes in protease activity were monitored by azocasein degradation. In the second and third phase rumen undegradable protein (UDP) was digested with pepsin and pancreatin, respectively. The measurements showed that 63.2, 5.2 and 4.7% of the crude protein of green lucerne was decomposed by rumen fluid, pepsin and pancreatin, respectively. Degradability of the crude protein of extracted sunflower meal was 68.3, 17.7 and 5.5% in the three phases, respectively. Repeated determination yielded crude protein degradabilities of 66.7, 27.1 and 5.1% for the three phases, respectively.  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