全文获取类型
收费全文 | 3756篇 |
免费 | 159篇 |
国内免费 | 3篇 |
专业分类
林业 | 235篇 |
农学 | 94篇 |
基础科学 | 27篇 |
640篇 | |
综合类 | 610篇 |
农作物 | 119篇 |
水产渔业 | 326篇 |
畜牧兽医 | 1578篇 |
园艺 | 101篇 |
植物保护 | 188篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 35篇 |
2021年 | 66篇 |
2020年 | 72篇 |
2019年 | 91篇 |
2018年 | 85篇 |
2017年 | 100篇 |
2016年 | 84篇 |
2015年 | 59篇 |
2014年 | 91篇 |
2013年 | 193篇 |
2012年 | 219篇 |
2011年 | 284篇 |
2010年 | 160篇 |
2009年 | 140篇 |
2008年 | 275篇 |
2007年 | 278篇 |
2006年 | 256篇 |
2005年 | 261篇 |
2004年 | 238篇 |
2003年 | 215篇 |
2002年 | 199篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 37篇 |
1998年 | 32篇 |
1997年 | 28篇 |
1996年 | 23篇 |
1995年 | 33篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 12篇 |
1988年 | 21篇 |
1987年 | 30篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1977年 | 8篇 |
1974年 | 4篇 |
1973年 | 8篇 |
1970年 | 3篇 |
1904年 | 2篇 |
排序方式: 共有3918条查询结果,搜索用时 0 毫秒
1.
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
2.
3.
Mark G Papich 《Veterinary Clinics of North America: Equine Practice》2003,19(3):645-63, vi
Antibiotics will always be needed in horses for many types of infections, but the adverse consequences also must be considered. For the conditions described in this article, there is justification for antibiotic therapy. The intestinal problems that antibiotics can induce are among the risks from their administration to horses. Disruption of the endogenous bacterial population, colitis, and diarrhea are the most common complications from antibiotic therapy. 相似文献
4.
5.
Mark A Oyama 《Veterinary Clinics of North America: Small Animal Practice》2004,34(5):1083-104, v
Echocardiography is an exceptionally useful technique for diagnosing cardiovascular disease in small animals. It is noninvasive and provides a wealth of data concerning cardiac morphology and function. For many patients, echocardiography is the definitive diagnostic tool. A well-performed study coalesces the findings of the physical examination, electrocardiogram, and radiographs into a clearly defined diagnosis on which treatment decisions can be based. More so than other diagnostic techniques, echocardiography is highly operator dependent and relies on the proper acquisition and interpretation of results by an examiner who is familiar with the principles, capabilities, and limitations of ultrasound imaging.This article reviews the basics of echocardiography, measurement of cardiac dimensions, and assessment of cardiac function. Within these sections, emerging technologies that expand the capabilities of the echocardiographic examination are introduced. 相似文献
6.
Mark Thornley 《Australian veterinary journal》2004,82(12):722-722
7.
8.
Shanice R. MajorClifford L. Fontenot Jr. John A. Pojman Sr.John A. Pojman Jr. Mark E. Merchant 《Comparative immunology, microbiology and infectious diseases》2011,34(2):115-121
Some animals routinely endure serious injuries from predators or during intraspecific territorial conflicts. Such is the case for Amphiuma tridactylum, an aquatic salamander that lives in an environment rich in potentially infectious microbes, apparently with rare or no pathogenic infection. Some vertebrates possess innate immune mechanisms, but whether this is the case for Amphiuma is unknown. To assess this potential, plasma from 19 A. tridactylum was pooled and used for characterisation of serum complement activity. The ability of A. tridactylum plasma to hemolyse unsensitised sheep red blood cells (SRBCs) was titer-dependent, with low activity observed even at high plasma titers. The kinetic characterisation of SRBC hemolysis revealed that significant activity could be measured within 10 min of incubation, and maximal activity occurred within 60 min. The SRBC hemolysis by A. tridactylum plasma was also temperature-dependent, with maximal activity at 30 °C. In addition, this activity was sensitive to mild heat treatment, with 96% of activity inhibited by incubation at 56 °C for 30 min. The SRBC hemolysis could also be inactivated by pretreatment of the plasma with proteases, indicating that this activity was protein dependent. The activity required divalent metals ions, with activity inhibited by EDTA, citrate, or phosphate. However, the chelator-inhibited activity could be restored by the addition of excess Ca2+ or Mg2+, but not Cu2+ or Ba2+, indicating specificity of the divalent metal ion requirement. The sensitivity to heat, proteases, and divalent metal ion chelators strongly suggests that A. tridactylum plasma-mediated hemolysis of SRBCs is mediated by the serum complement system of proteins. 相似文献
9.
M Craddick R Patel A Lower S Highlander M Ackermann D McClenahan 《Veterinary immunology and immunopathology》2012,149(1-2):58-65
Mannheimia haemolytica, one of the agents associated with bovine respiratory disease complex, can cause severe lung pathology including the leakage of vascular products into the airways and alveoli. Previous work by this laboratory has demonstrated that bovine lung endothelial and epithelial cells undergo dramatic permeability increases when exposed to adenosine-5'-triphosphate (ATP). Therefore, we wanted to determine if ATP levels were elevated in bronchoalveolar lavage (BAL) samples from calves experimentally infected with M. haemolytica. In addition, cultured bovine pulmonary epithelial (BPE) cells were stimulated with heat-killed and live M. haemolytica bacteria, lipopolysaccharide (LPS), lipoteichoic acid (LTA), interleukin-1 (IL-1), and zymosan activated plasma (ZAP) to determine whether they might release extracellular ATP during in vitro infection. Calves experimentally exposed to M. haemolytica had an approximately 2-fold higher level of ATP in their BAL samples compared to control. BPE cells exposed to increasing numbers of heat-killed or live M. haemolytica had significantly increased levels of ATP release as compared to time-matched controls. Finally, BPE cells treated with several concentrations of LPS and IL-1 had increases in ATP release as compared to time-matched controls. This increase appeared to be a result of active ATP secretion by the cells, as cell viability was similar between treated and non-treated cells. Neither ZAP nor LTA induced any ATP release by the cells. In conclusion, ATP levels are elevated in lung secretions from calves infected with M. haemolytica. In addition, lung epithelial cells can actively release ATP when exposed to heat-killed or live M. haemolytica, LPS or IL-1. 相似文献
10.
Three approaches for multivariate analysis of fish growth in aquaculture experiments with Nile tilapia (Oreochromis niloticus niloticus L.) based on the von Bertalanffy growth curve are presented and compared. The approaches are: an extended Gulland‐and‐Holt (GH) plot, a forced extended GH plot and a multilinear regression analysis for the growth parameter K. All three models provide valuable insight into the major environmental factors influencing the daily growth rate and explain 28–46% of the variance of the observed daily growth rate of the used data set. For all three methods, the modelled parameter is significantly related to the net yield of Nile tilapia and can, therefore, be used for the predictive modelling of management scenarios. The extended GH plot loads the influence of environmental parameters upon L∞, while the forced extended GH plot and Direct fitting of K load the influence on the growth parameter K. The latter is more in the tradition of aquaculture research. But the forced extended GH plot and Direct fitting of K can only be applied if L∞ of the cultured species is known, as the selected L∞ influences the variance in the regression variables. 相似文献