全文获取类型
收费全文 | 14197篇 |
免费 | 1175篇 |
国内免费 | 4篇 |
专业分类
15376篇 |
出版年
2022年 | 92篇 |
2021年 | 222篇 |
2020年 | 153篇 |
2019年 | 200篇 |
2018年 | 212篇 |
2017年 | 203篇 |
2016年 | 339篇 |
2015年 | 507篇 |
2014年 | 653篇 |
2013年 | 788篇 |
2012年 | 952篇 |
2011年 | 993篇 |
2010年 | 603篇 |
2009年 | 593篇 |
2008年 | 763篇 |
2007年 | 802篇 |
2006年 | 770篇 |
2005年 | 711篇 |
2004年 | 682篇 |
2003年 | 660篇 |
2002年 | 639篇 |
2001年 | 210篇 |
2000年 | 147篇 |
1999年 | 187篇 |
1998年 | 164篇 |
1997年 | 138篇 |
1996年 | 124篇 |
1995年 | 134篇 |
1994年 | 97篇 |
1993年 | 136篇 |
1992年 | 133篇 |
1991年 | 104篇 |
1990年 | 128篇 |
1989年 | 105篇 |
1988年 | 89篇 |
1987年 | 93篇 |
1986年 | 79篇 |
1985年 | 99篇 |
1984年 | 115篇 |
1983年 | 96篇 |
1982年 | 133篇 |
1981年 | 102篇 |
1980年 | 84篇 |
1979年 | 76篇 |
1978年 | 83篇 |
1977年 | 66篇 |
1976年 | 59篇 |
1975年 | 54篇 |
1974年 | 78篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Chlorotetracycline inhibits the uncoupled oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L.) mitochondria extensively (over 80%) and rapidly (inhibition complete in 10 s) in the presence of added Ca2+. Half-maximal inhibition is observed at 15 μM chlorotetracycline in the presence of 2 mM Ca2+. The oxidation of succinate is only affected marginally by chlorotetracycline plus Ca2+. The inhibition of NADH oxidation and the fluorescence of CTC are well correlated. Mn2+ is the only other cation which shows an (increased) inhibition in the presence of chlorotetracycline. The inhibition by Ca2+ and chlorotetracycline disappears at acid pH, and the pH optimum in their presence is 6.4. The inhibition caused by other lipid-soluble Ca2+-chelators is not reversible or is enhanced by the addition of excess Ca2+. In contrast, inhibition caused by relatively water-soluble chelators is completely reversed by added Ca2+. It is suggested that a neutral 1:2 complex is formed between Ca2+ and chlorotetracycline which can substitute for Ca2+ bound at sites in the lipophilic phase of the inner mitochondrial membrane, which are essential for the activity of the external NADH dehydrogenase. 相似文献
93.
Measurements of dNTP pools following exposure of Chinese hamster ovary cells to ultraviolet radiation reveals a rapid accumulation of cellular dTTP and a rapid loss of cellular dCTP. Exposure to 3-, 10- or 20 Jm-2 results in a 3-, 4- or 5.4-fold increase in cellular dTTP, respectively, within the first 10 min after exposure. dTTP levels then decrease noticeably, approaching the control value 3 to 5 hr later. In contrast, dCTP levels decrease rapidly within 10 min after exposure, ultimately to 1/10 that observed in the unirradiated control population. Recovery to normal dCTP levels is slow, taking in excess of 12 hr. No change in dATP is observed for 1-2 hr; subsequently, a moderate decrease in dATP levels occurs which is then followed by recovery, beginning 8 hr after irradiation. These results contrast with changes in dNTP pools observed in Chinese hamster V-79 cells exposed to mutagens. Measurements of rates of DNA synthesis by pulse-labeling cells with [3H]thymidine are also apparently affected by UV-induced transient deviations in the endogenous radiospecific activity of the labeled precursor. 相似文献
94.
Effects of Nitrogen Sources on Cellulose and Synthetic Lignin Degradation by Phanerochaete chrysosporium 总被引:4,自引:4,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ian D. Reid 《Applied microbiology》1983,45(3):838-842
Phanerochaete chrysosporium degraded cellulose faster with organic nitrogen sources than with NH4Cl. Simple and complex nitrogen sources added at the time of inoculation to N-limited cultures of P. chrysosporium, with glucose as carbon/energy source, transiently stimulated degradation of synthetic [14C]lignin to 14CO2. The same nitrogen sources added 5 days after inoculation, when the cultures were entering secondary metabolism, delayed 14CO2 production. The various N sources affected synthetic lignin degradation in defined medium differently than lignin degradation in aspen wood. 相似文献
95.
96.
Specificity of the Na+-dependent monocarboxylic acid transport pathway in rabbit renal brush border membranes 总被引:7,自引:0,他引:7
Edward P. Nord Stephen H. Wright Ian Kippen Ernest M. Wright 《The Journal of membrane biology》1983,72(3):213-221
The substrate specificity of a Na+-dependent transport pathway for L-lactate was studied in rabbit renal brush border membrane vesicles. Jmax for L-lactate transport was unaffected by the presence of a fixed concentration of two different short-chain monocarboxylic acids, while the apparent Kt(Ka) for L-lactate increased, and this is compatible with competitive inhibition. The inhibitor constants ("Ki"'s) for the transport pathway for the two solutes examined closely corresponded to the respective "Ki"'s derived from a Dixon plot. A broad range of compounds were then tested as potential inhibitors of L-lactate transport, and the "Ki"'s thereby derived yielded specific information regarding optimal substrate recognition by the carrier. A single carboxyl group is an absolute requirement for recognition, and preference is given to 3 to 6 C chain molecules. Addition of ketone, hydroxyl and, particularly, amine groups at any carbon position, diminishes substrate-carrier interaction. Intramolecular forces, notably the inductive effects of halogens, may play a role in enhancing substrate-carrier interaction; however, no correlation was found between pKa and "Ki" for the substrates examined. We conclude that a separate monocarboxylic acid transport pathway, discrete from either the D-glucose, alpha or beta neutral amino-acid, or dicarboxylic acid carriers, exists in the renal brush border, and this handles a broad range of monocarboxylates. 相似文献
97.
James W. Cosgrove John J. Heikkila Alexander Marks Ian R. Brown 《Journal of neurochemistry》1983,40(3):806-813
Abstract: Free and membrane-bound polysomes were isolated from the cerebral hemispheres and cerebellum of the young adult rabbit. The two polysomal populations were translated in an mRNA-dependent cell-free system derived from rabbit reticulocytes. Analysis of the [35 S]methionine-labeled translation products on two-dimensional polyacrylamide gels indicated an efficient separation of the two classes of brain polysomes. The relative synthesis of S100 protein by free and membrane- bound polysomes was determined by direct immuno-precipitation of the cell-free translation products in the presence of detergents to reduce nonspecific trapping. Synthesis of S100 protein was found to be twofold greater on membrane-bound polysomes compared with free polysomes isolated from either the cerebral hemispheres or the cerebellum. In addition, the proportion of poly- (A+)mRNA coding for SlOO protein was also twofold greater in membrane-bound polysomes compared with free polysomes isolated from the cerebral hemispheres. These results indicate that the cytoplasmic S100 protein is synthesized predominantly on membrane-bound polysomes in the rabbit brain. We suggest that the nascent S100 polypeptide chain translation complex is attached to the rough endoplasmic reticulum by an ionic interaction involving a sequence of 13 basic amino acids in S100 protein. 相似文献
98.
The H-2
dm1
mutation and Qa antigens 总被引:2,自引:0,他引:2
P. Mark Hogarth Ian D. Walker Aveline J. Rigby Ian F. C. McKenzie 《Immunogenetics》1983,18(6):617-624
The effect of the H-2dm1 mutation on Qa-m2 expression was examined. The mutant strain B10.D2-H-2dm1 showed a fourfold increase in Qa-m2 expression when compared with the parental strain B10.D2. Qa-m2 molecules immunoprecipitated from B10.D2-H-2dm1, C57BL/10, and B10.D2 spleen cells were identical by two-dimensional (2-D) gel electrophoresis [isoelectric focusing (IEF) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE]). It is likely therefore that the increased Qa-m2 expression is not due to gross structural alterations of the Qa-m2 molecule; in the present study, alternative explanations are discussed. 相似文献
99.
Anders Fjose Ian F. Pryme Johan R. Lillehaug 《Molecular and cellular biochemistry》1983,56(2):137-144
Summary After transfer of Krebs II ascites cells from the mouse peritoneum to suspension culture addition of the phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate (TPA) causes an early stimulation of 3H-choline incorporation into phosphatidylcholine (PC). Choline transport into the treated cells, however, was unaffected. Within 30 min of TPA treatment 3H-choline incorporation was almost 300% above the control level. During a 5 hr period of suspension culture the overall patterns of 3H-choline incorporation were similar in TPA-treated and control cultures though the rate was greatly accentuated by the presence of the phorbol ester. Incubation of cells with cycloheximide prior to incubation with TPA did not result in an inhibition of the TPA-directed 3H-choline incorporation. After 3 hr incubation with TPA there were large increases in radioactivity in all subcellular fractions. At 20 hr, however, the values were not far from those of the control. During the first 3 hr of incubation with TPA the incorporation of 3H-choline into light rough (LR) and smooth (S) membranes was stimulated to levels of 400% and 320% respectively above control values. At later times the profiles of radioactivity in membrane subfractions in TPA-treated and control cultures were similar. The results illustrate an early effect of TPA on PC biosynthesis in Krebs II ascites cells while at later times of incubation the stimulatory effect was virtually abolished. 相似文献
100.