全文获取类型
收费全文 | 20028篇 |
免费 | 1831篇 |
国内免费 | 19篇 |
出版年
2022年 | 118篇 |
2021年 | 264篇 |
2020年 | 133篇 |
2019年 | 208篇 |
2018年 | 262篇 |
2017年 | 207篇 |
2016年 | 381篇 |
2015年 | 675篇 |
2014年 | 746篇 |
2013年 | 928篇 |
2012年 | 1209篇 |
2011年 | 1280篇 |
2010年 | 776篇 |
2009年 | 670篇 |
2008年 | 969篇 |
2007年 | 1076篇 |
2006年 | 995篇 |
2005年 | 982篇 |
2004年 | 973篇 |
2003年 | 946篇 |
2002年 | 922篇 |
2001年 | 215篇 |
2000年 | 151篇 |
1999年 | 218篇 |
1998年 | 265篇 |
1997年 | 192篇 |
1996年 | 176篇 |
1995年 | 208篇 |
1994年 | 182篇 |
1993年 | 169篇 |
1992年 | 172篇 |
1991年 | 149篇 |
1990年 | 140篇 |
1989年 | 131篇 |
1988年 | 139篇 |
1987年 | 140篇 |
1986年 | 141篇 |
1985年 | 160篇 |
1984年 | 180篇 |
1983年 | 151篇 |
1982年 | 217篇 |
1981年 | 224篇 |
1980年 | 224篇 |
1979年 | 143篇 |
1978年 | 149篇 |
1977年 | 134篇 |
1976年 | 166篇 |
1975年 | 124篇 |
1974年 | 139篇 |
1973年 | 155篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
231.
232.
233.
234.
235.
Passive Electrical Properties of Microorganisms: V. Low-Frequency Dielectric Dispersion of Bacteria 总被引:2,自引:0,他引:2 下载免费PDF全文
Very high dielectric constants have been observed for bacteria at low frequencies. High dielectric constants such as these can be explained by a theory which has been developed for the low-frequency dielectric dispersion of porous charged particles and which has been tested successfully through measurements with ion exchange resins. The bacterial cell wall is electrically similar to an ion exchange resin. Observations show that the theory provides a quantitative explanation for the low-frequency dielectric dispersion of bacteria. 相似文献
236.
L.Charles Dickinson James C.W. Chien 《Biochemical and biophysical research communications》1973,51(3):587-592
Single crystals of horse CoHb were obtained by reduction of CoHb+ crystals with dithionite. Epr measurements showed that the g? and Coà tensors are both axial and share the same principal axis systems. Of the four subunits, the “heme” normals of C? and d? subunits ãb?plane 29 ± 1° from b?; they have the same orientation as the hemes in methemoglobin. The normals of “hemes” à and B? are 47 above the ãb? plane as compared to 16° in methemoglobin. 相似文献
237.
The karyotypes of 200 normal individuals are examined in a study designed to investigate the extent to which the cytologist's classification of chromosomes into the A–G autosomal groups and identification of individual chromosomes are reflected in the values of measurements made on these chromosomes. The statistical technique of discriminant function analysis is employed to obtain linear functions of the chromosomal measurements which may be used to classify and identify chromosomes. The results of the study indicate that while chromosomes can be grouped with a reasonably high probability of success using measurements alone, identification of individual chromosomes is somewhat more difficult. 相似文献
238.
A simple and safe procedure has been described for the preparation of short-chain aliphatic hydroxamic acids in quantities as large as 1 mole and as small as 0.01 mole. The procedure is equally suitable for the preparation of isotopically labeled hydroxamates, as has been demonstrated in the case of 1-14C-acetohydroxamic acid and 3H-acetohydroxamic acid. Some physical and chemical characteristics, including infrared spectra of formo-, aceto-, propiono-, and isobutyro-hydroxamic acids prepared by this method have been described. 相似文献
239.
ION-INDUCED ULTRASTRUCTURAL TRANSFORMATIONS IN ISOLATED MITOCHONDRIA : The Energized Uptake of Calcium 总被引:10,自引:4,他引:6 下载免费PDF全文
The energized uptake of low levels of Ca2+ in the presence and absence of phosphate by isolated rat liver mitochondria, and the perturbation effected by this activity on ultrastructural and metabolic parameters of mitochondria have been investigated. In the presence of phosphate, low levels of Ca2+ are taken up by mitochondria and result in various degrees of ultrastructural expansion of the inner mitochondrial compartment. This indicates that low levels of Ca2+ in the presence of phosphate, are accumulated in an osmotically active form into the water phase of the inner compartment. The first clearly observable quantitative increase in the volume of the inner compartment occurs after the accumulation of 100 nmoles Ca2+/mg protein. An accumulation of 150–200 nmoles Ca2+/mg protein, which is equivalent to the osmolar concentration of endogenous K+, is required to effect a doubling of the volume of the inner compartment. This degree of osmotic perturbation occurs as mitochondria transform from a condensed to an orthodox conformation. The osmotically induced orthodox conformation differs from the mechanochemically induced orthodox conformation previously described, in that its development is concomitant with a marked decrease in acceptor control and oxidative phosphorylation efficiency and it fails to transform to a condensed conformation in response to addition of ADP. In the absence of added phosphate, a maximum of 190 nmoles Ca2+/mg protein was found to be taken up by mitochondria (state 6). Ca2+ is apparently bound under state 6 conditions since the uptake does not effect an ultrastructural expansion of the inner compartment. Phosphate added after state 6 Ca2+ binding, however, results in an immediate ultrastructural expansion of the inner compartment. The addition of phosphate to mitochondria in the absence of exogenous Ca2- fails to effect an osmotic ultrastructural transformation. Under state 6 conditions, the binding of between 40 and 190 nmoles Ca2+/mg protein results in the formation of dense matrix inclusions which appear to be composed of tightly packed, concentrically oriented membranes. Under conditions in which the bound Ca2+ is subsequently released, there is a concomitant loss in the density of these matrix inclusions, leaving behind morphologically distinct membrane whorls in the mitochondrial matrix. 相似文献
240.
Biosynthesis of Riboflavine in Corynebacterium Species: the Purine Precursor 总被引:4,自引:3,他引:1 下载免费PDF全文
Corynebacterium species lacks the ability to convert either xanthine or guanine to adenine. This defect and the use of the purine nucleoside antibiotic decoyinine, which blocks the conversion of xanthosine monophosphate --> guanosine monophosphate, permit an experimental design in which the interconversion of purines is largely prevented. Cultures of this organism were grown in the presence of decoyinine and various purine supplements. Data obtained by comparing the radioactivity incorporated from guanine-2-(14)C or xanthine-2-(14)C into bacterial guanine, xanthine, and riboflavine indicate that guanine or a close derivative of guanine is the purine precursor of riboflavine. 相似文献