全文获取类型
收费全文 | 1244篇 |
免费 | 60篇 |
专业分类
林业 | 98篇 |
农学 | 188篇 |
基础科学 | 30篇 |
245篇 | |
综合类 | 85篇 |
农作物 | 82篇 |
水产渔业 | 69篇 |
畜牧兽医 | 376篇 |
园艺 | 37篇 |
植物保护 | 94篇 |
出版年
2022年 | 15篇 |
2021年 | 21篇 |
2020年 | 35篇 |
2019年 | 19篇 |
2018年 | 41篇 |
2017年 | 47篇 |
2016年 | 38篇 |
2015年 | 36篇 |
2014年 | 38篇 |
2013年 | 91篇 |
2012年 | 68篇 |
2011年 | 64篇 |
2010年 | 49篇 |
2009年 | 50篇 |
2008年 | 55篇 |
2007年 | 41篇 |
2006年 | 31篇 |
2005年 | 30篇 |
2004年 | 24篇 |
2003年 | 22篇 |
2002年 | 27篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 21篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 17篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1979年 | 25篇 |
1978年 | 11篇 |
1975年 | 13篇 |
1973年 | 11篇 |
1972年 | 10篇 |
1970年 | 14篇 |
1969年 | 18篇 |
1968年 | 11篇 |
1967年 | 13篇 |
排序方式: 共有1304条查询结果,搜索用时 31 毫秒
101.
102.
Expression of lactate and malate dehydrogenases in tumors induced by SV40 and 7,12-dimethylbenz(a)anthracene 总被引:1,自引:0,他引:1
Isozyme patterns of lactate and malate dehydrogenases were studied in tumors induced by SV40 and 7,12-dimethylbenz(a)anthracene and in established cultures of cells from these tumors. The expression of B polypeptide subunits of lactate dehydrogenase is suppressed similarly by both agents. This may be due to inactivation of the gene at the locus determining the B polypeptide subunit. Malate dehydrogenase isozyme patterns are not changed significantly by the virus or the carcinogen. 相似文献
103.
A G protein mutant that inhibits thrombin and purinergic receptor activation of phospholipase A2 总被引:7,自引:0,他引:7
The stimulation of phospholipase A2 by thrombin and type 2 (P2)-purinergic receptor agonists in Chinese hamster ovary cells is mediated by the G protein Gi. To delineate alpha chain regulatory regions responsible for control of phospholipase A2, chimeric cDNAs were constructed in which different lengths of the alpha subunit of Gs (alpha s) were replaced with the corresponding sequence of the Gi alpha subunit (alpha i2). When a carboxyl-terminal chimera alpha s-i(38), which has the last 38 amino acids of alpha s substituted with the last 36 residues of alpha i2, was expressed in Chinese hamster ovary cells, the receptor-stimulated phospholipase A2 activity was inhibited, although the chimera could still activate adenylyl cyclase. Thus, alpha s-i(38) is an active alpha s, but also a dominant negative alpha i molecule, indicating that the last 36 amino acids of alpha i2 are a critical domain for G protein regulation of phospholipase A2 activity. 相似文献
104.
Thallium ion-induced carbonyl carbon chemical shifts were compared for all of the L-residue-peptide carbonyl carbons of the gramicidin A transmembrane channel. Molecular structures were deduced by using the argument that helically equivalent and equally proximal carbonyls would exhibit essentially equivalent ion-induced chemical shifts. The transmembrane channel was found to be a head-to-head dimer with the structure of a left-handed, single-stranded beta-helix. 相似文献
105.
Matter described by quantum chromodynamics (QCD), the theory of strong interactions, may undergo phase transitions when its temperature and the chemical potentials are varied. QCD at finite temperature is studied in the laboratory by colliding heavy ions at varying beam energies. We present a test of QCD in the nonperturbative domain through a comparison of thermodynamic fluctuations predicted in lattice computations with the experimental data of baryon number distributions in high-energy heavy ion collisions. This study provides evidence for thermalization in these collisions and allows us to find the crossover temperature between normal nuclear matter and a deconfined phase called the quark gluon plasma. This value allows us to set a scale for the phase diagram of QCD. 相似文献
106.
Hong D Gupta R Ancliff P Atzberger A Brown J Soneji S Green J Colman S Piacibello W Buckle V Tsuzuki S Greaves M Enver T 《Science (New York, N.Y.)》2008,319(5861):336-339
Understanding cancer pathogenesis requires knowledge of not only the specific contributory genetic mutations but also the cellular framework in which they arise and function. Here we explore the clonal evolution of a form of childhood precursor-B cell acute lymphoblastic leukemia that is characterized by a chromosomal translocation generating a TEL-AML1 fusion gene. We identify a cell compartment in leukemic children that can propagate leukemia when transplanted in mice. By studying a monochorionic twin pair, one preleukemic and one with frank leukemia, we establish the lineal relationship between these "cancer-propagating" cells and the preleukemic cell in which the TEL-AML1 fusion first arises or has functional impact. Analysis of TEL-AML1-transduced cord blood cells suggests that TEL-AML1 functions as a first-hit mutation by endowing this preleukemic cell with altered self-renewal and survival properties. 相似文献
107.
Climate reconstructions reveal unprecedented warming in the past century; however, little is known about trends in aspects such as the monsoon. We reconstructed the monsoon winds for the past 1000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea and found that monsoon wind strength increased during the past four centuries as the Northern Hemisphere warmed. We infer that the observed link between Eurasian snow cover and the southwest monsoon persists on a centennial scale. Alternatively, the forcing implicated in the warming trend (volcanic aerosols, solar output, and greenhouse gases) may directly affect the monsoon. Either interpretation is consistent with the hypothesis that the southwest monsoon strength will increase during the coming century as greenhouse gas concentrations continue to rise and northern latitudes continue to warm. 相似文献
108.
We demonstrate the ability to measure the energy required to flip the spin of single adsorbed atoms. A low-temperature, high-magnetic field scanning tunneling microscope was used to measure the spin excitation spectra of individual manganese atoms adsorbed on Al2O3 islands on a NiAl surface. We find pronounced variations of the spin-flip spectra for manganese atoms in different local environments. 相似文献
109.
110.
Sundareshwar PV Murtugudde R Srinivasan G Singh S Ramesh KJ Ramesh R Verma SB Agarwal D Baldocchi D Baru CK Baruah KK Chowdhury GR Dadhwal VK Dutt CB Fuentes J Gupta PK Hargrove WW Howard M Jha CS Lal S Michener WK Mitra AP Morris JT Myneni RR Naja M Nemani R Purvaja R Raha S Vanan SK Sharma M Subramaniam A Sukumar R Twilley RR Zimmerman PR 《Science (New York, N.Y.)》2007,316(5822):204-205