全文获取类型
收费全文 | 203224篇 |
免费 | 10600篇 |
国内免费 | 140篇 |
专业分类
林业 | 8605篇 |
农学 | 6305篇 |
基础科学 | 1363篇 |
24972篇 | |
综合类 | 36536篇 |
农作物 | 8216篇 |
水产渔业 | 9700篇 |
畜牧兽医 | 102644篇 |
园艺 | 2649篇 |
植物保护 | 12974篇 |
出版年
2019年 | 1839篇 |
2018年 | 2696篇 |
2017年 | 3070篇 |
2016年 | 2830篇 |
2015年 | 2364篇 |
2014年 | 2971篇 |
2013年 | 7941篇 |
2012年 | 5585篇 |
2011年 | 6938篇 |
2010年 | 4581篇 |
2009年 | 4636篇 |
2008年 | 6920篇 |
2007年 | 6446篇 |
2006年 | 6036篇 |
2005年 | 5706篇 |
2004年 | 5579篇 |
2003年 | 5637篇 |
2002年 | 5244篇 |
2001年 | 6132篇 |
2000年 | 6201篇 |
1999年 | 4822篇 |
1998年 | 2150篇 |
1997年 | 2094篇 |
1996年 | 1952篇 |
1995年 | 2361篇 |
1994年 | 2152篇 |
1993年 | 2009篇 |
1992年 | 4110篇 |
1991年 | 4387篇 |
1990年 | 4239篇 |
1989年 | 4241篇 |
1988年 | 3916篇 |
1987年 | 3918篇 |
1986年 | 4091篇 |
1985年 | 3982篇 |
1984年 | 3224篇 |
1983年 | 2937篇 |
1982年 | 1950篇 |
1979年 | 3036篇 |
1978年 | 2454篇 |
1977年 | 2001篇 |
1976年 | 2039篇 |
1975年 | 2147篇 |
1974年 | 2611篇 |
1973年 | 2728篇 |
1972年 | 2602篇 |
1971年 | 2471篇 |
1970年 | 2314篇 |
1969年 | 2275篇 |
1967年 | 1951篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
F Urayama T Sato H Shibuya W Shirai M Matsutani R Yamazaki 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2001,63(11):1249-1252
An apocrine adenocarcinoma was observed in the subcutis of the abdomen of golden hamster. Histologically, the tumor cells irregularly formed multiple layers of cysts and some detached cells were presented in the cystic space. PAS stain with alpha-amylase digestion revealed PAS-positive alpha-amylase-resistant granules in the cytoplasm. Immunohistochemically, cytokeratin was demonstrated in the tumor cells. By electron microscopy, the tumor cells had an oval nucleus with invagination, abundant cytoplasmic organelles and microvilli protruding into the intercellular spaces. 相似文献
82.
Abstract. Leaching losses of nitrate-nitrogen were measured from a set of eight hydrologically isolated plots on a clay loam soil over the period from September 1987 to February 1990. Variable drainflow recovery from the plots hampered accurate estimation of nitrate loading, but results suggest that, when inorganic nitrogen fertilizer is applied up to the recommended amount, there is little influence of the amount applied on the amount leached. We did, however, observe the following effects on nitrate leaching: leguminous green manure incorporated in autumn increased leaching of nitrate-nitrogen by 10–15 kg per hectare during the winter; autumn cultivation caused some increase in leaching compared with no cultivation in one year; some systematic variations in nitrate leaching occurred between years and between plots, but were unrelated to treatments.
From the results we conclude that green manuring does not provide sufficient nitrogen for organically grown crops on this soil but contributes significantly to nitrate leaching, and that growing spring cereals, with the land remaining in stubble as long as possible in autumn, may be the best strategy to minimize nitrate leaching. 相似文献
From the results we conclude that green manuring does not provide sufficient nitrogen for organically grown crops on this soil but contributes significantly to nitrate leaching, and that growing spring cereals, with the land remaining in stubble as long as possible in autumn, may be the best strategy to minimize nitrate leaching. 相似文献
83.
L A Wyant 《Veterinary Clinics of North America: Equine Practice》2001,17(2):297-303
The Internet is a fast-growing technology that allows information (text as well as images) to be shared across the world in an instant. As computer systems, software, and Internet services become less expensive options, the world becomes more experienced and comfortable with these technologies. In the foreseeable future, equine veterinarians are likely to be better educated about diseases and treatments, better connected with specialists for consultations on difficult cases, able to respond to client communications more efficiently, able to accurately educate clients, and able to communicate with colleagues from across the country and the world. Additionally, there is likely to be a time when using the Internet and computers is profitable in all these ways as well as economically. Improving doctor-client relationships and patient care are goals for all veterinarians, and the Internet holds the technology to render these now and in the future. 相似文献
84.
R. Thomassen 《Reproduction in domestic animals》1993,28(4):289-293
Contents: An insemination trial using frozen semen is described. The freezing procedure was slightly modified from the Hannover method. The insemination dose consisted of 7 medium straws containing approx 1 109 spermatozoa. A total of 28 mares of the Norwegian Trotter breed were inseminated during the 1991 season. During oestrus the mares were examined at 12 hour intervals, and the insemination was carried out after detection of ovulation. The pregnancy rate was 43% after the first insemination, increased to 68% after second and further to 75% after the third and last insemination. The foaling rate was 61.5%. 相似文献
85.
86.
Jamie S. Harmon Kim G. Michelsen Dr. Mark A. Sheridan 《Fish physiology and biochemistry》1991,9(4):361-368
Trialcylglycerol (TG) lipase was isolated and partially purified from rainbow trout liver. Triacylglycerol lipase activity was assayed by measuring14C-oleic acid release from14C-triolein.14C-oleic acid release was linear for up to two hours. Optimal activity occurred at pH 7.0 and 15°C. Most of the lipase activity was recovered in the cytosolic fraction. A 27,000-fold purification was achieved after Sepharose (Bio-gel A 0.5 M, 200–400 mesh) chromatography of a resuspended 20% ammonium sulfate fraction. The molecular weight of the trout hepatic lipase as determined by size-exclusion chromatography and by SDS-polyacrylamide gel electrophoresis was 40–43 kD. Lipase-mediated hydrolysis of TG resulted in the production of diacylglycerols, monoacylglycerols, and fatty acids. Kinetic analysis indicated that Vmax=0.016 nmol/h/mg protein and that Km=0.28 mM triolein. Lipolytic activity was enhanced in the presence of cAMP/ATP-Mg2+. These results suggest that the liver of trout possesses a neutral TG lipase that is responsible for mobilizing stored TG and is catalytically activated by phosphorylation.A part of this work was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1990, San Antonio, TX. 相似文献
87.
The technique of cystocentesis in dogs and cats was studied. The indications and contraindications of this method are discussed, using illustrations. 相似文献
88.
Time course of grain filling pattern in two rice (Oryza sativa L.) cultivars, grown under normal and low light intensities, was studied. The number of spikelets, partially filled grains and high density grains were monitored at a 5 day interval during grain filling period from uniform panicles tagged at anthesis. The low light tolerant cultivar Swarnaprabha had more high density grains and less partially filled grains throughout the grain filling period and at harvest compared to cultivar Ratna under both normal and low light intensities. Further, the opening of spikelets in two flushes in Swarnaprabha seemed to result in a more efficient resource allocation and hence better yield as compared to Ratna, in which the opening of spikelets was in a single flush on day 10. 相似文献
89.
A Desrochers D E Anderson G St-Jean 《Veterinary Clinics of North America: Food Animal Practice》2001,17(1):143-58, vii
Digital diseases are commonly seen in cattle. Cattle affected by digital disorders do not always respond to conservative therapy and require surgery. Surgical procedures for the common digital disorders are described, with emphasis on the different approaches to the distal interphalangeal joint. 相似文献
90.
J Tetens S A Barker M Waguespack G Hosgood 《Canadian journal of veterinary research》2001,65(2):133-135
The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period. 相似文献