全文获取类型
收费全文 | 6176篇 |
免费 | 557篇 |
国内免费 | 4篇 |
出版年
2023年 | 18篇 |
2022年 | 51篇 |
2021年 | 126篇 |
2020年 | 82篇 |
2019年 | 100篇 |
2018年 | 133篇 |
2017年 | 119篇 |
2016年 | 185篇 |
2015年 | 309篇 |
2014年 | 309篇 |
2013年 | 483篇 |
2012年 | 493篇 |
2011年 | 469篇 |
2010年 | 312篇 |
2009年 | 267篇 |
2008年 | 386篇 |
2007年 | 420篇 |
2006年 | 354篇 |
2005年 | 340篇 |
2004年 | 297篇 |
2003年 | 299篇 |
2002年 | 297篇 |
2001年 | 64篇 |
2000年 | 44篇 |
1999年 | 64篇 |
1998年 | 66篇 |
1997年 | 47篇 |
1996年 | 46篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 35篇 |
1991年 | 24篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 21篇 |
1983年 | 12篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 10篇 |
1975年 | 15篇 |
1974年 | 11篇 |
1965年 | 10篇 |
排序方式: 共有6737条查询结果,搜索用时 15 毫秒
1.
Ouenzar Bouchra Hartmann Caroline Rode Andre Benslimane Abdelali 《Plant Molecular Biology Reporter》1998,16(3):263-269
We have developed a new mini-procedure for isolation of total cellular DNA from date palm (Phoenix dactylifera L.). The procedure, which does not use liquid nitrogen, has proved useful due to temporary disruptions in supplies of liquid nitrogen that occur in countries where date palm trees are cultivated. DNA suitable for RFLP and PCR analyses is obtained. 相似文献
2.
Se-Chan Kim Alexander Ghanem Heidi Stapel Klaus Tiemann Pascal Knuefermann Andreas Hoeft Rainer Meyer Christian Grohé Anne A Knowlton Georg Baumgarten 《BMC physiology》2007,7(1):5
Backgound
It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT). 相似文献3.
Pascal Griesmar Clément Sanchez Germain Puccetti Isabelle Ledoux Joseph Zyss 《Molecular Engineering》1991,1(3):205-220
Orientation of optically nonlinear organic molecules inside sol-gel matrices upon application of an external D.C. electrical field is demonstrated for the first time. The quadratic nonlinear response of silicon oxide or transition metal oxide based gels containing organic molecules has been determined from Electric Field Induced Second Harmonic (EFISH) measurements. Large concentrations of Optically Nonlinear Organic Molecules (ONOM) have been either incorporated inside the macromolecular network or chemically bonded to the oxide backbone of the gels. These results demonstrate the feasibility of permanently poled doped sol-gel matrices. Moreover, EFISH measurements performed on organic molecules appear to be a useful tool for monitoring the changes occurring during sol-gel transformations. 相似文献
4.
5.
Determination of stereochemistry in the fatty acid hydroperoxide products of lipoxygenase catalysis 总被引:1,自引:0,他引:1
High-performance liquid chromatography has been found to be an effective method for the determination of absolute configuration in the products of the lipoxygenase-catalyzed oxygenation of polyunsaturated fatty acids. Methyl esters of fatty acid hydroperoxides that had been reduced to the corresponding alcohols were converted into (+)-alpha-methoxy-alpha-trifluoromethylphenylacetic acid esters. Enantiomeric alcohols were converted into diastereomeric esters that were readily resolved by normal-phase HPLC. The instrumental requirements for the technique are an isocratic HPLC and a uv absorbance monitor. The method was found to be effective in the determination of stereochemistry in the products derived from the action of plant lipoxygenases on linoleic acid. In addition, the chromatography of the derivatives obtained from lipoxygenase catalysis on arachidonic acid was found to be effective for the assignment of stereochemistry in those products. A comparison of the chromatography of these derivatives with that for the corresponding menthyloxycarbonyl derivatives demonstrated the superiority of this approach for the resolution of the diastereomeric pairs. The technique was applied to the determination of stereochemistry in the products derived from soybean lipoxygenase isoenzymes under a variety of experimental conditions. 相似文献
6.
The influence of He-Ne laser radiation (632.8 nm, 56 J/m2, t = 10 s) and phytohaemagglutinin (PHA, 2 micrograms/ml) on chromatin structure in human lymphocytes was studied by electron microscopy using ultrathin cell sections. Morphometric analysis of extranuclear condensed chromatin masses was performed 1 h after the irradiation or after the beginning of PHA treatment. In the irradiated cells the following insignificant changes were revealed: decrease in the relative area of the nucleoplasmic chromatin, increase in the relative area of decondensation zones as well as increase in the number of clumps of nucleoplasmic chromatin and relative length at their boundary with nucleoplasma. The tendency of these morphological changes may be interpreted as functional activation of extranucleolar RNA synthesis in response to irradiation by red laser light. Action of PHA results in significant changes of the surfaces of chromatin clumps, namely increase in relative length of nucleoplasmic chromatin boundary and decrease in relative length of perimembranous chromatin boundary with nucleoplasma as well as some less expressed delamination of the chromatin masses from the nuclear membrane. These essential changes may reflect chromatin activation by proliferative stimulus. Peculiarities of the ultrastructural reorganisation in the condensed chromatin after irradiation and PHA-treatment probably reflect the differences in the processes of gene activation caused by the two agents. 相似文献
7.
Jeffrey P Mower Pascal Touzet Julie S Gummow Lynda F Delph Jeffrey D Palmer 《BMC evolutionary biology》2007,7(1):135
Background
It has long been known that rates of synonymous substitutions are unusually low in mitochondrial genes of flowering and other land plants. Although two dramatic exceptions to this pattern have recently been reported, it is unclear how often major increases in substitution rates occur during plant mitochondrial evolution and what the overall magnitude of substitution rate variation is across plants. 相似文献8.
Often we must balance being prepared to act quickly with being prepared to suddenly stop. The stop signal task (SST) is widely used to study inhibitory control, and provides a measure of the speed of the stop process that is robust to changes in subjects’ response strategy. Previous studies have shown that preparation affects inhibition. We used fMRI to separate activity that occurs after a brief (500 ms) warning stimulus (warning-phase) from activity that occurs during responses that follow (response-phase). Both of these phases could contribute to the preparedness to stop because they both precede stop signals. Warning stimuli activated posterior networks that signal the need for top-down control, whereas response phases engaged prefrontal and subcortical networks that implement top-down control. Regression analyses revealed that both of these phases affect inhibitory control in different ways. Warning-phase activity in the cerebellum and posterior cingulate predicted stop latency and accuracy, respectively. By contrast, response-phase activity in fronto-temporal areas and left striatum predicted go speed and stop accuracy, in pre-supplementary motor area affected stop accuracy, and in right striatum predicted stop latency and accuracy. The ability to separate hidden contributions to inhibitory control during warning-phases from those during response-phases can aid in the study of models of preparation and inhibitory control, and of disorders marked by poor top-down control. 相似文献
9.
10.