全文获取类型
收费全文 | 4253篇 |
免费 | 320篇 |
国内免费 | 1篇 |
出版年
2021年 | 38篇 |
2020年 | 22篇 |
2019年 | 42篇 |
2018年 | 32篇 |
2017年 | 50篇 |
2016年 | 72篇 |
2015年 | 105篇 |
2014年 | 137篇 |
2013年 | 197篇 |
2012年 | 245篇 |
2011年 | 231篇 |
2010年 | 149篇 |
2009年 | 126篇 |
2008年 | 206篇 |
2007年 | 242篇 |
2006年 | 195篇 |
2005年 | 172篇 |
2004年 | 183篇 |
2003年 | 182篇 |
2002年 | 158篇 |
2001年 | 91篇 |
2000年 | 81篇 |
1999年 | 83篇 |
1998年 | 61篇 |
1997年 | 64篇 |
1996年 | 48篇 |
1995年 | 40篇 |
1994年 | 35篇 |
1993年 | 44篇 |
1992年 | 56篇 |
1991年 | 58篇 |
1990年 | 50篇 |
1989年 | 49篇 |
1988年 | 53篇 |
1987年 | 41篇 |
1986年 | 50篇 |
1985年 | 49篇 |
1984年 | 40篇 |
1983年 | 31篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 33篇 |
1979年 | 36篇 |
1978年 | 30篇 |
1977年 | 25篇 |
1976年 | 30篇 |
1973年 | 25篇 |
1972年 | 19篇 |
1971年 | 19篇 |
1968年 | 19篇 |
排序方式: 共有4574条查询结果,搜索用时 328 毫秒
121.
Karl Wilhelm Heinz Comtesse Walter Pflumm 《Ethology : formerly Zeitschrift fur Tierpsychologie》1982,60(1):27-40
Different concentrations of a sucrose solution vary the courtship song and behaviour of the male yellow-bellied sunbird Nectarinia venusta- the duration of subsong, total singing duration, and the absolute number of full song phrases. With high concentrations the sunbird sings more full song phrases but less subsong during the courtship season than otherwise. The various effects are described. 相似文献
122.
Transacylation as a chain-termination mechanism in fatty acid synthesis by mammalian fatty acid synthetase. Synthesis of medium-chain-length (C8-C12) acyl-CoA esters by goat mammary-gland fatty acid synthetase. 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. Ruminant mammary-gland fatty acid synthetases can, in contrast with non-ruminant mammary enzymes, synthesize medium-chain fatty acids. 2. Medium-chain fatty acids are only synthesized in the presence of a fatty acid-removing system such as albumin, beta-lactoglobulin or methylated cyclodextrin. 3. The short- and medium-chain fatty acids synthesized were released as acyl-CoA esters from the fatty acid synthetase. 相似文献
123.
The breeding performance of captive willow ptarmigan on different diets has been studied. The nutritional factors tested were protein concentration, natural feed supplement and grass meal and flavonoid admixture, and effects on egg numbers, fertility, hatchability, chick weights at hatching and 0–14 days mortality have been recorded. The breeding performance of ptarmigan hen in captivity showed great individual variations. Egg numbers were not statistically different in groups fed the different diets. Hens fed a 15 % crude protein died tended to produce smaller chicks with significantly lower viability than chicks from hens fed a 20 % crude protein diet. Supplement of natural feed tended to increase the number of chicks hatched through a combination of tendency to higher egg numbers and improved fertility. These tendencies were, however, statistically nonsignificant. Inclusion of 34 % grass meal to the diet also tended (non-significantly) to improve fertility and hatchability, while inclusion of flavonoids had no positive effect on reproduction. Eggs from captive hens showed significantly lower fertility, and a tendency to lower hatchability than eggs from wild hens. The former difference was probably caused by the close cage confinements for the captive ptarmigan, while the latter condition probably was due to different start of incubation, most of the eggs from wild hens being started naturally. 相似文献
124.
The marked effects of ethylene on pea stem growth have been investigated. Low temperature and colchicine, both known microtubule depolymerization agents, reverse the effects of ethylene in straight growth tests. Low temperature (6 C) also profoundly reduces the effects of gas in terms of swelling, hook curvature, and horizontal nutation. Deuterium oxide, an agent capable of rigidifying microtubular structure, mimics the effects of ethylene. Electron microscopy shows that microtubule orientation is strikingly altered by ethylene. These findings indicate that some of the ethylene responses may be due to a stabilizing effect on microtubules in plant cells. 相似文献
125.
Lactose carrier protein of Escherichia coli. Structure and expression of plasmids carrying the Y gene of the lac operon 总被引:53,自引:0,他引:53
R M Teather J Bramhall I Riede J K Wright M Fürst G Aichele U Wilhelm P Overath 《European journal of biochemistry》1980,108(1):223-231
The previously described hybrid plasmid pC7 which carries lacI+O+delta(Z)Y+A+ on a 12.3 X 10(6)-Mr DNA fragment [Teather et al. (1978) Mol. Gen. Genet. 159, 239-248] was partially digested with the restriction endonuclease EcoRI under conditions reducing the recognition sequence to d(A-A-T-T) and ligated to the vector pB322. lac Y-carrying inserts of various sized (Mr 1.5-4.7 X 10(6)) were obtained. Hybrid plasmid pTE18 (2300-base-pair insert) carries part of the I (repressor) gene, the promotor-operator region, part of the Z (beta-galactosidase) gene, the Y (lactose carrier) gene and part of the A (transacetylase) gene. Upon induction of pTE18-harbouring strains the Y-gene product is expressed at a nearly constant rate for several generations and accumulates to a level of 12-16% of the total cytoplasmic membrane protein. Integration into the membrane leads to active carrier as judged by binding and transport measurements. 相似文献
126.
Characteristics of a simple, high-resolution flow cytometer based o a new flow configuration.
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A method is described for the quantitative determination of free and bound solute concentrations in the cytoplasm of intact cells. The method includes (a) introduction of a gelatin gel reference phase (RP) into the cytoplasm; (b) diffusion of dissolved substances between cytoplasm and RP, (c) cell quenching to - 196 degrees C to prevent subsequent solute redistributions, (d) ultra-low temperature microdissection to isolate RP and cytoplasm samples, and (e) analysis of isolates for solute and water content. In normal oocytes of the salamander, Desmognathus ochrophaeus, free or RP Na+ and K+ are 21.0 +/- 1.1 and 128.8 +/- 2.4 mu eq/ml, respectively, and vary stoichiometrically in altered oocytes. Overall cytoplasmic concentrations are 75.2 +/- 2.7 mu eq Na+/ml and 88.6 +/- 1.5 mu eq K+/ml. Cytoplasmic chemical activities are 16.2 mu eq Na+/ml and 99.2 mu eq K+/ml, corresponding to activity coefficients of 0.22 and 1.12, respectively. The results demonstrate unambiguously that (a) oocytes actively transport Na+ and K+, and (b) cytoplasm has important binding properties which differentiate it from an ordinary aqueous solution. These cytoplasmic properties are investigated in the following paper. 相似文献
127.
Medium-chain fatty acid synthesis in lactating-rabbit mammary gland. Intracellular concentration and specificity of medium-chain acyl thioester hydrolase.
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J Knudsen 《The Biochemical journal》1979,181(2):267-274
The concentration of medium-chain acyl thioester hydrolase and of fatty acid synthetase was determined by rocket immunoelectrophoresis in nine different particle-free supernatant fractions from lactating-rabbit mammary gland. The molar ratio of the hydrolase to fatty acid synthetase was 1.99 +/- 0.66 (mean +/- S.D.). A rate-limiting concentration of malonyl-CoA was required to ensure the predominant synthesis of medium-chain fatty acids when 2 mol of the hydrolase was added per mol of fatty acid synthetase. The interaction of the hydrolase with fatty acid synthetase was concentration-dependent, though an optimum concentration of hydrolase to synthetase could not be obtained. The lactating-rabbit mammary gland hydrolase altered the pattern of fatty acids synthesized by fatty acid synthetases prepared from cow, goat, sheep and rabbit lactating mammary glands, rabbit liver and cow adipose tissue. 相似文献
128.
Steen Pedersen Solveig V. Reeh Jack Parker Robert J. Watson James D. Friesen Niels P. Fiil 《Molecular & general genetics : MGG》1976,144(3):339-343
Summary The presence of EF-Tu, RNA polymerase subunit , and EF-G on the dfus-3 genome and EF-Tu, ribosomal proteins L7/L12, and RNA polymerase subunit on the drif
d
18 genome has been confirmed using a two-dimensional gel electrophoresis technique sensitive to changes in isoelectric point and molecular weight. In this system two EF-Tu gene products could not be resolved. Following infection of ultraviolet light-irradiated Escherichia coli with either dfus-3 or drif
d
18, the EF-Tu gene, tufA, near 65 minutes on the genetic map is expressed as 3–4 copies per EF-G molecule. The EF-Tu gene, tufB, near 79 minutes on the genetic map, is expressed at about one-third of this rate. is expressed as 1 copy per EF-G molecule, as 0.14 per EF-G molecule and L7/L12 as 2.5 per EF-G. These figures compare well with the relative amounts found in exponentially-growing cells, in which the ratio of EF-Tu to EF-G is approximately 5. Almost 90% of the total number of proteins (calculated on a molecular weight basis) which theoretically can be encoded on the drif
d
18 have been identified on the two-dimensional gel. 相似文献
129.
Summary Senescence occurs in all wild strains of Podospora anserina after continued growth. This syndrome can be inhibited by a synergistic interaction of two linked genes, incoloris and vivax. Whereas the wild strain starts to become senescent after 26 d and the mutants incoloris and vivax after 42 and 66 d respectively, the double mutant shows no signs of aging after culture for more than one year. 相似文献
130.
Immunofluorescence microscopy using monospecific tubulin antibody shows that in vivo griseofulvin interferes with the expression of both cytoplasmic and spindle microtubules in tissue culture cells in a concentration-dependent manner. In mouse 3T3 cells cytoplasmic microtubules are destroyed at a griseofulvin concentration of 5 × 10?5m. At this concentration no increase of the mitotic index is observed but the cells are arrested in interphase, probably due to the destruction of cytoplasmic microtubules. Lowering the drug concentration to 10?5m allows 3T3 cells to accumulate in c-mitotic (“colchicin-mitotic”) arrest. In HeLa cells the display of spindle microtubules observed in drug-arrested cells appears similar to that seen in normal metaphase cells only at lower griseofulvin concentrations. Higher drug concentrations induce c-mitotic arrest accompanied by an increasing loss of typical metaphase tubulin structures.In vitro polymerization experiments with brain tubulin using both light-scattering and electron microscopy show that in the presence of griseofulvin tubulin can aggregate rapidly in the cold. This behaviour is not found in the absence of the drug. Thus both in vivo and in vitro experiments show that griseofulvin, like other c-mitotic drugs, acts at the level of tubulin polymerization and that its effects are concentration dependent. 相似文献