全文获取类型
收费全文 | 1067208篇 |
免费 | 112529篇 |
国内免费 | 432篇 |
专业分类
1180169篇 |
出版年
2018年 | 10113篇 |
2017年 | 9710篇 |
2016年 | 13682篇 |
2015年 | 17736篇 |
2014年 | 20965篇 |
2013年 | 30624篇 |
2012年 | 34152篇 |
2011年 | 35037篇 |
2010年 | 23793篇 |
2009年 | 22067篇 |
2008年 | 31301篇 |
2007年 | 32366篇 |
2006年 | 30483篇 |
2005年 | 29179篇 |
2004年 | 28955篇 |
2003年 | 27855篇 |
2002年 | 27185篇 |
2001年 | 45388篇 |
2000年 | 45079篇 |
1999年 | 36586篇 |
1998年 | 13640篇 |
1997年 | 13937篇 |
1996年 | 13273篇 |
1995年 | 12274篇 |
1994年 | 12040篇 |
1993年 | 12068篇 |
1992年 | 30367篇 |
1991年 | 29603篇 |
1990年 | 29000篇 |
1989年 | 28503篇 |
1988年 | 26217篇 |
1987年 | 25114篇 |
1986年 | 23463篇 |
1985年 | 23496篇 |
1984年 | 19353篇 |
1983年 | 16947篇 |
1982年 | 12898篇 |
1981年 | 11654篇 |
1980年 | 11044篇 |
1979年 | 18394篇 |
1978年 | 14474篇 |
1977年 | 13055篇 |
1976年 | 12421篇 |
1975年 | 13761篇 |
1974年 | 14661篇 |
1973年 | 14491篇 |
1972年 | 13178篇 |
1971年 | 11858篇 |
1970年 | 10396篇 |
1969年 | 10060篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
M Janowski L Baugnet-Mahiec J Merregaert L de Saint-Georges A Sassen J N Ihle J R Maisin 《Comptes rendus des séances de la Société de biologie et de ses filiales》1980,174(5):832-839
Two distinct rat propagates of a radiation leukemia virus (RadLV-Rs) from the C57BL mouse respectively induced characteristic leukemogenic effects. These were found to be related with the infection titers of the isolates, but not with either their antigenic specificities or their viral and proviral genome sequences. 相似文献
983.
984.
By means of the histostereometrical method, peculiarities of the thyroid gland formation have been studied in the lemming (Dicrostonyx torquatus) fetuses and newborns at the stage of the population quantity drop, as well specificity of the organ's morphofunctional state during the postnatal period. On the 14th prenatal day the thyroid gland already has the follicular structure. Up to the 19th day progressive follicular growth, accumulation of colloid and increase of its density occur. On the 19th-20th days, as well as in newborn animals, there are certain signs, demonstrating as essential activation of the thyroid gland function. In the newborn animals cavities of the completely formed follicles are devastated. During the postnatal period again growth of follicles, accumulation of colloid are observed, signs of hypersecretion of the hypophysis appear. 相似文献
985.
Jonathan D. Nickels Joseph E. Curtis Hugh O’Neill Alexei P. Sokolov 《Journal of biological physics》2012,38(3):497-505
Recent studies have discovered strong differences between the dynamics of nucleic acids (RNA and DNA) and proteins, especially at low hydration and low temperatures. This difference is caused primarily by dynamics of methyl groups that are abundant in proteins, but are absent or very rare in RNA and DNA. In this paper, we present a hypothesis regarding the role of methyl groups as intrinsic plasticizers in proteins and their evolutionary selection to facilitate protein dynamics and activity. We demonstrate the profound effect methyl groups have on protein dynamics relative to nucleic acid dynamics, and note the apparent correlation of methyl group content in protein classes and their need for molecular flexibility. Moreover, we note the fastest methyl groups of some enzymes appear around dynamical centers such as hinges or active sites. Methyl groups are also of tremendous importance from a hydrophobicity/folding/entropy perspective. These significant roles, however, complement our hypothesis rather than preclude the recognition of methyl groups in the dynamics and evolution of biomolecules. 相似文献
986.
Human long-latency auditory evoked potentials were studied during simulation with variable-amplitude pulse sequences from a sound source moving to and from the subject. The N1 peak parameters were shown to depend on an accurate estimate of the direction of the change in the distance to the sound source. Differences in the processing of signals that simulated the approaching and/or distancing of the sound source were found in the N1 and P2 component parameters of on- and off-responses as was a more pronounced long negative potential shift in the evoked response to the approaching source as compared to the distancing source. 相似文献
987.
Yeast cell mortality related to a high-pressure shift: occurrence of cell membrane permeabilization 总被引:3,自引:0,他引:3
The shrinkage of yeast cells caused by high-pressure treatment (250 MPa, 15 min) was investigated using direct microscopic observation. A viable staining method after treatment allowed the volume variation of two populations to be distinguished: an irreversible volume decrease (about 35% of the initial volume) of pressure-inactivated cells during pressure holding time, and viable cells, which were less affected. A mass transfer was then induced during high-pressure treatment. Causes of this transfer seem to be related to a pressure-induced membrane permeabilization, allowing a subsequent leakage of internal solutes, where three ions (Na+, K+ and Ca2+), plus endogenous glycerol, were verified. This glycerol leakage was found to occur after yeast pressurization in a medium having low water activity, although the yeast was not inactivated. All these observations lead to the hypothesis that pressure-induced cell permeabilization could be the cause of yeast inactivation under pressure. 相似文献
988.
O. V. Yagodina E. B. Nikol’skaya I. Y. Shemarova A. E. Khovanskikh 《Journal of Evolutionary Biochemistry and Physiology》2000,36(3):244-248
A comparison has been performed of catalytic properties of unicellular microorganism amine oxidases (AO) from two new enzyme
sources, the bacteriumMethanosarcina barkeri and the infusoriaTetrahymena pyriformis. It was shown that the both studied AO deaminate tyramine, serotonin, and benzylamine, but do not deaminate histamine. The
AO fromMethanosarcina barkeri catalyzes deamination of all three substrates at an identical rate, while the rate of tyramine deamination under effect of
AO fromTetrahymena pyriformis is one order higher than the rate of serotonin deamination, and about two orders higher than the rate of benzylamine deamination.
Based on the data of the substrate-inhibitor analysis, a suggestion was made about the existence of one center for the substrate
binding in the AO of the studied bacterium, while several centers in the AO of the studied infusoria. 相似文献
989.
A rapid, sensitive, assay for enzymes that degrade heparin is described. The procedure is based on the interference of heparin with color development during the interaction of protein with the dye Coomassie brilliant blue. The loss of this property when the glycosaminoglycan is degraded by heparinase can be used to quantify activity of the enzyme in pure form, or in complex biological samples such as tissue homogenates or serum. The assay is also suitable for studying dependence of heparinase activity under conditions such as varying pH and temperature. 相似文献
990.
K Scheuch W D Pietruschka E Hentschel P Winiecki G Gruber 《Activitas nervosa superior》1988,30(3):169-173
Biochemical and immunological parameters, physical and mental performance, subjective complaints and behavioural characteristics were compared before and after 14 final examinations undertaken by 64 students during a three-month examination period. A decrease in cholesterol, triglycerides, HDL-cholesterol, physical performance and an increase in LDL/HDL cholesterol quotient, lactate level, mental performance were accompanied by a lower frequency of mental complaints and higher frequency of physical complaints. From the multidimensional variance and discriminant analysis 17 of the 44 variables discriminated between the state prior to and after the examination period. The results are interpreted in terms of the psychophysiological adaptation to adequate mental stress. 相似文献