全文获取类型
收费全文 | 102815篇 |
免费 | 4838篇 |
国内免费 | 48篇 |
专业分类
林业 | 7333篇 |
农学 | 4078篇 |
基础科学 | 696篇 |
13321篇 | |
综合类 | 14936篇 |
农作物 | 5566篇 |
水产渔业 | 6024篇 |
畜牧兽医 | 46293篇 |
园艺 | 2010篇 |
植物保护 | 7444篇 |
出版年
2018年 | 3787篇 |
2017年 | 3865篇 |
2016年 | 2331篇 |
2015年 | 1064篇 |
2014年 | 1312篇 |
2013年 | 3309篇 |
2012年 | 3065篇 |
2011年 | 4776篇 |
2010年 | 3877篇 |
2009年 | 3054篇 |
2008年 | 4062篇 |
2007年 | 4148篇 |
2006年 | 2477篇 |
2005年 | 2432篇 |
2004年 | 2293篇 |
2003年 | 2479篇 |
2002年 | 2166篇 |
2001年 | 2640篇 |
2000年 | 2595篇 |
1999年 | 2048篇 |
1998年 | 863篇 |
1997年 | 953篇 |
1995年 | 1027篇 |
1994年 | 864篇 |
1993年 | 876篇 |
1992年 | 1727篇 |
1991年 | 1904篇 |
1990年 | 1859篇 |
1989年 | 1866篇 |
1988年 | 1741篇 |
1987年 | 1657篇 |
1986年 | 1771篇 |
1985年 | 1653篇 |
1984年 | 1445篇 |
1983年 | 1239篇 |
1982年 | 863篇 |
1979年 | 1384篇 |
1978年 | 1030篇 |
1977年 | 978篇 |
1976年 | 918篇 |
1975年 | 983篇 |
1974年 | 1242篇 |
1973年 | 1240篇 |
1972年 | 1231篇 |
1971年 | 1143篇 |
1970年 | 1093篇 |
1969年 | 1052篇 |
1968年 | 895篇 |
1967年 | 986篇 |
1966年 | 817篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
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
33.
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
34.
Matthew M. Nelson Ben D. Mooney Peter D. Nichols Charles E Phleger Greg G. Smith Piers Hart Arthur J. Ritar 《Journal of the World Aquaculture Society》2002,33(2):146-157
The lipid class and fatty acid (FA) composition of juvenile Artemia fed continuously on four diets—the microalga Tetraselmis suecica , a mix of oat bran-wheat germ-lecithin (OWL), OwL-eicosapentaenoic acid (EPA), and OWL-EPA-arachidonic acid (AA)—were examined over a 9-d experiment in an attempt to approximate the FA profile of phyllosoma larvae of wild southern rock lobster Jasus edwardrii . The main difference in lipid class composition of Artemia fed the four diets was the relative level of polar lipid (PL) and triacylglycerol (TAG). By day 9, the algal-fed Artemia were highest in PL (95% of total lipid) and lowest in TAG (2%), whereas the remaining diets resulted in Artemia with 16–30% PL and 41–82% TAG. After 2 d, the relative FA composition of all Artemia treatments closely reflected those of the diets, with no marked change after further feeding (to day 9). In terms of the content of essential polyunsaturated fatty acids (PUFA), by day 5 Artemia fed: 1) with the algal diet contained 7 mg/g FA dry mass (0.3% DHA, 6.3% EPA, 3.4% AA of total FA); 2) with the OWL diet contained 3 mg/g (0.3% DHA, 0.9% EPA, 0.7% AA); 3) with the OWL-EPA diet contained 55 mg/g (6.2% DHA, 11.6% EPA, 1.1% AA); and 4) with the OWL-EPA-AA contained 83 mg/g (3.8% DHA, 7.5% EPA, 17.4% AA). The PUFA profiles of Artemia using the OWL-oil diets were similar to wild rock lobster phyllmmata, although levels of doco-sahexaenoic acid (DHA) were lower (10% DHA) than in J. edwardsii larvae. On the basis of PUFA composition data alone, the results suggest the suitability of the OWL-oil mixed diets for consideration for feeding to Artemia used in the culture of southern rock lobster larvae, particularly if the level of DHA can be further enhanced. 相似文献
35.
36.
37.
G R Johnston P A Walter D A Feeney 《Veterinary Clinics of North America: Small Animal Practice》1986,16(2):261-292
Radiopaque uroliths and nonradiopaque (water density) uroliths are filling defects encountered in the urinary tracts of dogs and cats. Other free luminal and attached soft tissue density filling defects encountered during uroradiographic special procedures include blood clots, air bubbles, hematomas, granulomas, abscesses, inflammatory and neoplastic polyps. Nonradiopaque uroliths cannot be identified on survey radiographs from other soft tissue dense structures. Gray scale ultrasonography can be used to differentiate nonradiopaque (water dense) uroliths from other soft tissue attached or free luminal filling defects of the excretory pathway. The differential radiographic features of filling defects encountered during cystography and urethrography are described and illustrated. 相似文献
38.
39.
40.
Techniques for in vitro production of embryos have been developed world-wide in different species, with promising results in human and ruminants. Thousands of human IVF-babies have been born during the last 20 years and thousands of in vitro -produced calves have been born since the late 1980s. With current methods for bovine in vitro fertilization, about 30–40% of in vitro -fertilized bovine oocytes develop further to the blastocyst stage and can be used for transfer. A proper evaluation of blastocyst quality remains however, an important challenge for every researcher involved in embryology and for every clinician who wants to select the best embryos for transfer. This review attempts to summarize the different methods available for estimation of blastocyst quality with a special emphasis upon differential staining. 相似文献