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   96316篇
  免费   5773篇
  国内免费   42篇
林业   3976篇
农学   3067篇
基础科学   562篇
  12030篇
综合类   16734篇
农作物   4058篇
水产渔业   4907篇
畜牧兽医   49023篇
园艺   1327篇
植物保护   6447篇
  2020年   804篇
  2019年   934篇
  2018年   1635篇
  2017年   1772篇
  2016年   1669篇
  2015年   1452篇
  2014年   1704篇
  2013年   3986篇
  2012年   3275篇
  2011年   3694篇
  2010年   2336篇
  2009年   2215篇
  2008年   3502篇
  2007年   3362篇
  2006年   3097篇
  2005年   2983篇
  2004年   2810篇
  2003年   2786篇
  2002年   2578篇
  2001年   3102篇
  2000年   2940篇
  1999年   2410篇
  1998年   1024篇
  1997年   930篇
  1996年   825篇
  1995年   1005篇
  1994年   893篇
  1993年   881篇
  1992年   1867篇
  1991年   1858篇
  1990年   1794篇
  1989年   1855篇
  1988年   1605篇
  1987年   1717篇
  1986年   1778篇
  1985年   1708篇
  1984年   1342篇
  1983年   1192篇
  1982年   856篇
  1979年   1136篇
  1978年   916篇
  1977年   791篇
  1976年   749篇
  1975年   821篇
  1974年   1020篇
  1973年   1059篇
  1972年   1014篇
  1971年   967篇
  1970年   912篇
  1969年   834篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Diagnosis, evaluation, and management of the various grades of rectal tears is discussed. Surgical techniques, which include direct closure, diverting colostomies, and placement of temporary rectal liners, are detailed. Also, rectal prolapses and various methods of repair are outlined.  相似文献   
92.
To identify antigens which may be important for stimulating immunity to pneumonic pasteurellosis, a bovine antiserum to whole P. haemolytica was used to screen a recombinant lambda gt11/P. haemolytica expression library. One of the recombinant bacteriophage clones identified with the bovine antiserum, SW20C, expressed a fusion protein which was also recognized by rabbit antiserum to partially purified P. haemolytica culture supernatant and was found to be immunogenic in guinea pigs. The guinea pig antibody recognized a 100 kDa protein in P. haemolytica cell lysates. Sequence analysis of the cloned DNA from SW20C identified a fragment of 1443 bp with a small open reading frame that was contiguous with the lacZ sequence. The 153 bp P. haemolytica-specific open reading frame encoded a polypeptide of approximately 6kDa. Homology searches of Genbank and the EMBL data bases revealed no homology of this open reading frame with any other bacterial sequences including P. haemolytica leukotoxin and Ssa1. Evaluation of sera from calves that were scored either susceptible or resistant to experimental pneumonic pasteurellosis demonstrated a significant (P < 0.001) correlation between the intensity of the antibody response to the SW20C antigen and resistance to disease.  相似文献   
93.
An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.  相似文献   
94.
95.
Dairy practice often requires substantial time commitments. Those veterinarians with families may find that if they do not actively budget some time for spouse and children, the family unit may suffer. A successful practice and meaningful family life are both possible if the doctor or doctors involved are willing to work for their achievement.  相似文献   
96.
The structure and ultrastructure of the adenohypophyseal pars distalis in kids of the Murciano-granadiana breed (18 males and 12 females), aged 2-3 months and with an average carcass weight of 8 kg has been studied. Techniques of staining (Tetrachrome Herlant's, and Cleveland-Wolfe) and histochemistry (PAS, PAS-OG and BA-PAS-OG) contrasted with immunolabelling (PAP) have been used. In addition an ultrastructural study has been made and nucleus and cytoplasm, secretory granules, mitochondria and lysosomes have been measured with a semiautomatic image analyzer (IBAS-1). TSH cells are found in sagittal section in the anterior area and in an antero-caudodorsal band, and transversally in the ventral and medial region; they are 6% and their average size is 14.15 microns. Ultrastructurally they are a single cellular type with spherical granules whose size is 195 nm in males and 149 in females; these granules are characterized by a clear halo and a variable electronic density. The rough endoplasmic reticulum is found as slightly enlarged vesicles with a homogeneous and moderately electro-dense content or in concentric stratifications.  相似文献   
97.
Three strip test kits which measure calcium and/or magnesium in mares' mammary secretions were compared and assessed for their accuracy in:- 1) measuring these electrolytes compared to standard laboratory measurements, and 2) predicting the time of parturition. Daily samples of mammary secretions were obtained pre-partum from 35 Thoroughbred mares and allocated a score. Measurement of mammary secretion calcium and/or magnesium by the strip tests and laboratory methods correlated significantly (P less than 0.001). The results obtained for prediction of parturition were analysed by two methods. Method i) indicated that the majority of mares had a maximum score on the day of birth. However, the second method of analysis included all prepartum scores and this demonstrated that maximum scores occurred on more occasions prior to the day of birth than on the day of birth itself. The number of nights spent attending mares, and the percentage of occasions when foaling was missed, were also calculated for given strip test scores. The results indicate that the test kits are not particularly accurate in predicting time of parturition although they are a reliable means of measuring mammary secretion calcium and/or magnesium. It is suggested that the test kits may be more helpful by indicating when it is not necessary to attend mares at night.  相似文献   
98.
The ultrastructure of sarcocysts of macro- and microscopic species of Sarcocystis was compared from naturally infected water buffalo from India. Grossly visible sarcocysts had walls consisting of cauliflower-like villar protrusions, typical of S. fusiformis. The sarcocyst wall of the microscopic species of Sarcocystis was 6.4 microns thick and consisted of tightly packed conical villar protrusions that were 9.6 microns long and 3.7 microns wide at the base. At approximately 3 microns above the base, the distal two-thirds of the villar protrusion became conical shaped and was bent laterally at an angle of 45 degrees to the sarcocyst surface. The granular layer beneath the villar protrusions was 0.9 microns thick. In S. levinei the granular layer was 1.9 microns thick, the villar protrusions were narrow and it had a highly undulating primary cyst wall. Whether the microscopic S. levinei-like sarcocysts of Indian and Malaysian water buffalo are distinct species of Sarcocystis will require further investigation.  相似文献   
99.
The influences of pelleting and beta-glucanase supplementation on the digestibility of dietary components in a barley-based diet were investigated in pigs fitted with cannulas in the terminal ileum. The diet contained 49.0% starch, 18.9% crude protein and 14.8% dietary fiber, with arabinoxylans (4.9%), mixed-linked beta-glucans (3.4%) and cellulose (3.3%) as the main fiber components. Pelleting increased mixed-linked beta-glucan solubility from 45 to 62%. Neither treatment influenced the ileal or fecal apparent digestibilities of dry matter (64 and 80%, respectively), energy (62 and 79%), crude protein (53 and 75%), crude fat (26 and 27%) or dietary fiber (58 and 72%). However, pelleting increased (P less than .01) the pre-ileal apparent digestibility of starch from 91.5 to 95.3% and decreased (P less than .03) that of ash from -10 to -23%, while increasing (P less than .005) the fecal apparent digestibility of starch from 98.6 to 99.7%. The solubility of mixed-linked beta-glucans in ileal digesta was lower (P less than .001) in pelleted (26%) than in unpelleted (58%) diets. beta-glucanase supplementation also increased (P less than .05) the ileal apparent digestibility of starch, from 92.6 to 94.3%, and of mixed-linked beta-glucans, from 95.7 to 97.1%. Significant between-pig differences in the apparent digestibility of dietary components were observed. In conclusion, treatments that disrupt the endosperm cell walls in barley can increase the proportion of the diet digested prior to the large intestine.  相似文献   
100.
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