全文获取类型
收费全文 | 1276036篇 |
免费 | 113945篇 |
国内免费 | 1473篇 |
专业分类
1391454篇 |
出版年
2021年 | 17693篇 |
2020年 | 12540篇 |
2019年 | 16092篇 |
2018年 | 16974篇 |
2017年 | 15755篇 |
2016年 | 27516篇 |
2015年 | 42004篇 |
2014年 | 50042篇 |
2013年 | 76268篇 |
2012年 | 33892篇 |
2011年 | 21416篇 |
2010年 | 42234篇 |
2009年 | 43975篇 |
2008年 | 20996篇 |
2007年 | 18566篇 |
2006年 | 24675篇 |
2005年 | 25821篇 |
2004年 | 25099篇 |
2003年 | 22933篇 |
2002年 | 20958篇 |
2001年 | 28367篇 |
2000年 | 25548篇 |
1999年 | 27154篇 |
1998年 | 24829篇 |
1997年 | 24681篇 |
1996年 | 24434篇 |
1995年 | 22476篇 |
1994年 | 22358篇 |
1993年 | 21433篇 |
1992年 | 24351篇 |
1991年 | 22788篇 |
1990年 | 21402篇 |
1989年 | 22451篇 |
1988年 | 20648篇 |
1987年 | 19859篇 |
1986年 | 18849篇 |
1985年 | 20832篇 |
1984年 | 21154篇 |
1983年 | 18862篇 |
1982年 | 19920篇 |
1981年 | 19306篇 |
1980年 | 17977篇 |
1979年 | 17691篇 |
1978年 | 16917篇 |
1977年 | 16284篇 |
1976年 | 15670篇 |
1975年 | 14961篇 |
1974年 | 15504篇 |
1973年 | 15779篇 |
1972年 | 13433篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
A.S. Tsaftaris J.C. Sorenson J.G. Scandalios 《Biochemical and biophysical research communications》1980,92(3):889-895
A protein isolated from maize scutella which inhibits catalase in vitro has been shown to contain 12% carbohydrate in the form of galactose. This corresponds to four galactose molecules per inhibitor subunit. Removal of the carbohydrate with β-galactosidase or blockage with a galactose-specific lectin abolished activity of the inhibitor. 相似文献
962.
W.M.F. Jongen P.H.M. Lohman M.J. Kottenhagen G.M. Alink F. Berends J.H. Koeman 《Mutation research》1981,81(2):203-213
Several short-term mammalian test systems were used for mutagenicity testing of the organic solvent dichloromethane. The compound was negative in the forward mutation test on the HGPRT locus in Chinese hamster cells and the unscheduled DNA synthesis test in both human and hamster cells. In the test on DNA synthesis inhibition, dichloromethane caused an aspecific inhibition in both human and hamster cells, but in this test the effect did not indicate a DNA-damaging action. A weak positive effect was found in the test on sister-chromatid exchanges in hamster cells. 相似文献
963.
964.
C. Sanderson 《BMJ (Clinical research ed.)》1974,1(5901):245-246
965.
966.
967.
The forty-two days long experiment was conducted on a total of 1000 Arbor Acres broilers, divided into two groups. Both groups
of broilers were fed with a commercial feed mixture which consisted of standard feedstuffs and contained enough nutrients
regarding the requirements. During the first three weeks of the trial, corn naturally contaminated with AFB1 0.0445 ppm per kg dry matter was used in the amount of 20% in the experimental group, while AFB1 free corn was given to birds in the control group. After the period of toxin administration until the end of the trial, broilers
from both groups were normally fed another 5 weeks with uncontaminated feed.
In the first phase of the trial, broilers in the control groups had an average daily gain (ADG) of 31 g, average daily feed
intake (ADFI) of 45 g and a feed: gain ratio (FCR) of 1.42. In the same time, experimental broilers achieved an ADG of 25
g, ADFI of 35 g and a FCR of 1.39. During the whole period of the trial, control and experimental broilers achieved 49.12
g, 95.24 g and 1.94 and 39.71 g, 86.90 g and 2.19, respectively. 相似文献
968.
Elena C. Guzman Alfonso Jimenez-Sanchez Elisha Orr Robert H. Pritchard 《Molecular & general genetics : MGG》1988,212(2):203-206
Summary A temperature shift-up accompanied by a reduction in RNA polymerase activity in Escherichia coli causes an increased rate of initiation leading to a 1.7- to 2.2-fold increase in chromosome copy number. A temperature shift-up without a reduction in polymerase activity induces only a transient non-scheduled initiation of chromosome replication caused by heat shock with no detectable effect on chromosome copy number. 相似文献
969.
STEVEN C. BEADLE 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1988,21(1):1-12
The cyclocrinitids are an extinct tribe of dasycladacean green algae. They were anatomically very similar to certain Recent dasyclads, even at early growth stages. The morphology and preservation of cyclocrinitids strongly suggest that they had a siphonous cellular organization with extracellular, aragonitic calcification; these features are characteristic of living dasyclads. The light surficial calcification of cyclocrinitids and other dasyclads had important paleoecological effects. It restricted them to low-energy waters, as it provided relatively little structural support. It also confined them to warm, tropical waters; they are good paleoequatorial indicators. The decline of these algae during the late Ordovician and early Silurian may therefore reflect the simultaneous cooling and glaciation. Receptaculitids are entirely unrelated organisms. Their meroms have several distinctive features; they are not homologous to the lateral branches of cyclocrinitids or dasyclads. Receptaculitid calcification was extensive and their thalli were apparently quite sturdy; they often occurred in reefs. Receptaculitids also lived in high-latitude, cold-water environments. Thus, they were ecologically unlike any calcareous green algae, and cannot be used as paleoequatorial indicators. Receptaculitids remain problematical, although the arrangement of meroms suggests plant affinities. □ Calcareous algae, Problematica, Dasycladales, Cyclocriniteae, Receptaculitales, morphology, classification, paleoecology, paleogeography . 相似文献
970.
Microsporidia 2003: IWOP-8 总被引:1,自引:0,他引:1
LOUIS M. WEISS 《The Journal of eukaryotic microbiology》2003,50(S1):566-568