全文获取类型
收费全文 | 386846篇 |
免费 | 37184篇 |
国内免费 | 273篇 |
专业分类
424303篇 |
出版年
2018年 | 8750篇 |
2017年 | 8585篇 |
2016年 | 7807篇 |
2015年 | 5564篇 |
2014年 | 6259篇 |
2013年 | 8778篇 |
2012年 | 12261篇 |
2011年 | 16913篇 |
2010年 | 12509篇 |
2009年 | 11728篇 |
2008年 | 14404篇 |
2007年 | 16317篇 |
2006年 | 8672篇 |
2005年 | 9434篇 |
2004年 | 8652篇 |
2003年 | 8602篇 |
2002年 | 8547篇 |
2001年 | 18252篇 |
2000年 | 18542篇 |
1999年 | 14100篇 |
1998年 | 4229篇 |
1997年 | 4509篇 |
1996年 | 4312篇 |
1995年 | 4002篇 |
1994年 | 3943篇 |
1993年 | 3805篇 |
1992年 | 11490篇 |
1991年 | 11142篇 |
1990年 | 10678篇 |
1989年 | 10253篇 |
1988年 | 9479篇 |
1987年 | 8849篇 |
1986年 | 8077篇 |
1985年 | 7959篇 |
1984年 | 6398篇 |
1983年 | 5571篇 |
1982年 | 4115篇 |
1981年 | 3590篇 |
1980年 | 3352篇 |
1979年 | 6108篇 |
1978年 | 4568篇 |
1977年 | 4123篇 |
1976年 | 3759篇 |
1975年 | 4337篇 |
1974年 | 4497篇 |
1973年 | 4389篇 |
1972年 | 4654篇 |
1971年 | 3988篇 |
1970年 | 3172篇 |
1969年 | 2968篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
T Nakano K Hanasaki S Matsumoto H Arita 《Biochemical and biophysical research communications》1988,154(3):1075-1080
All-trans-retinol induced aggregation of rabbit platelets, and this effect could be inhibited by a cyclooxygenase inhibitor and a thromboxane A2 (TXA2) receptor antagonist, indicating an essential role for endogenously produced TXA2. We found a two-phase arachidonic acid release in retinol-stimulated platelets. The first phase was induced by the action of retinol alone and not inhibited by TXA2 receptor antagonist. The second phase was induced via synergistic action of retinol and initially generated small amount of TXA2, and was inhibited by the antagonist. Moreover, we discussed that the arachidonic acid release may be mediated by the action of phospholipase A2. 相似文献
943.
V. S. Kurbanismailov O. A. Omarov G. B. Ragimkhanov M. Kh. Gadzhiev M. G. Bairkhanova A. J. Kattaa 《Plasma Physics Reports》2011,37(13):1166-1172
The experimental results on the formation and development of initial stages of an impulse breakdown in atmospheric-pressure
argon at townsend and streamer breakdown mechanisms for different initial conditions are presented. A streamer channel is
shown to be initiated by bright luminescence formed at the point of critical avalanche amplification at different distances
from the cathode depending on overvoltage. Prebreakdown currents are experimentally measured for the townsend and streamer
breakdown mechanisms and peculiarities of spark channel formation for these mechanisms are studied. 相似文献
944.
The radiosensitivity of cultured human and mouse keratinocytes 总被引:1,自引:0,他引:1
E K Parkinson W J Hume C S Potten 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1986,50(4):717-726
Clonogenic survival assays after gamma-radiation in vitro were performed on freshly isolated and subcultured keratinocytes from mouse skin, mouse tongue and human skin. Survival curves were constructed by fitting the data to a multi-target model of cell survival. When subcultured, keratinocytes from all sites produced survival curves which showed a reduced shoulder region and an increased D0 when compared with their freshly isolated counterparts. Freshly isolated human skin keratinocytes were more radiosensitive than mouse keratinocytes from either skin or tongue. 相似文献
945.
The paper analyzes humus profiles of mountain-chestnut soils of a complex catena situated within the Khemchik dry-steppe area
of the Central Tuva Depression. The study has shown that humus profile characteristics are determined by both slope aspects
and position in the catena. Humus profiles imprint all environmental changes of soil formation and functioning even if these
changes are not expressed in soil morphology. The materials obtained during the study may serve as basis for long-term monitoring
of slope soil behavior and for revealing local soil variability in changing environment. 相似文献
946.
Mamta Singhvi Dipti Joshi Shalaka Gaikaiwari Digambar V. Gokhale 《Indian journal of microbiology》2010,50(1):97-100
Method for production and regeneration of Lactobacillus delbrueckii protoplasts are described. The protoplasts were obtained by treatment with a mixture of lysozyme and mutanolysin in protoplast
buffer at pH 6.5 with different osmotic stabilizers. The protoplasts were regenerated on deMan, Rogosa and Sharpe (MRS) with
various osmotic stabilizers. Maximum protoplast formation was obtained in protoplast buffer with sucrose as an osmotic stabilizer
using a combination of lysozyme (1 mg/ml) and mutanolysin (10 μg/ml). Maximum protoplast regeneration was obtained on MRS
medium with sucrose (0.5 M) as an osmotic stabilizer. The regeneration medium was also applicable to other species of lactobacilli
as well. This is, to our knowledge, the first report on protoplast formation and efficient regeneration in case of L. delbrueckii. 相似文献
947.
It is generally perceived that landscape patterns or textures in a given protected area are spatially stationary. The findings
of this study suggest that this common perception is only partially correct. Over the course of 52 years, equilibrium in landscape
shifting was detected using digital data for the Lassen Volcanic National Park (USA). Vertical aerial photographs taken of
the park in 1941 were geo-referenced with the digital orthophoto quarter quadrangle (DOQQ) images of the same area from 1993
to identify landscape compositions and to measure change. Spatial analysis was used to observe pattern changes over time.
The results suggested that landscape development maintained equilibrium while patches were in various stages of a successional
sequence. The total area of each landscape component held steady, although over time patches throughout the landscape changed—a
shifting-mosaic steady state (SMSS). These findings reflect the limitations of contemporary environmental conservation theory.
They also suggest the importance of considering landscape change in policies that currently govern park planning and management. 相似文献
948.
Inactivation of Bacillus cereus spores during cooling (10 degrees C/h) from 90 degrees C occurred in two phases. One phase occurred during cooling from 90 to 80 degrees C; the second occurred during cooling from 46 to 38 degrees C. In contrast, no inactivation occurred when spores were cooled from a maximum temperature of 80 degrees C. Inactivation of spores at a constant temperature of 45 degrees C was induced by initial heat treatments from 80 to 90 degrees C. The higher temperatures accelerated the rate of inactivation. Germination of spores was required for 45 degrees C inactivation to occur; however, faster germination was not the cause of accelerated inactivation of spores receiving higher initial heat treatments. Repair of possible injury was not observed in Trypticase soy broth (BBL Microbiology Systems), peptone, beef extract, starch, or L-alanine at 30 or 35 degrees C. Microscopic evaluation of spores outgrowing at 45 degrees C revealed that when inactivation occurred, outgrowth halted at the swelling stage. Inhibition of protein synthesis by chloramphenicol at the optimum temperature also stopped outgrowth at swelling; thus protein synthesis may play a role in the 45 degree C inactivation mechanism. 相似文献
949.
950.
Substitutions of hydrophobic amino acids reduce the amyloidogenicity of Alzheimer's disease beta A4 peptides. 总被引:6,自引:0,他引:6
C Hilbich B Kisters-Woike J Reed C L Masters K Beyreuther 《Journal of molecular biology》1992,228(2):460-473
The deposition of amyloid protein aggregates in brain is the main pathological feature of Alzheimer's disease. Their principal constituent is a peptide termed beta A4, which comprises up to 43 amino acid residues. It is highly insoluble under physiological conditions and aggregates into filaments that form very dense clusters in vivo and in vitro. Based on a beta A4 prototype sequence spanning residues 10 to 42 or 43, we have designed analogues in which hydrophobic amino acid residues in position 17 to 20 were substituted by more hydrophilic residues. Depending on the kind of newly introduced amino acids and their position within the sequence, the substitution of only two residues led to variants exhibiting a broad spectrum of different properties. Common to them was a reduced beta-sheet content after solubilization in water and in the solid state. Some of the variants showed significantly reduced amyloidogenicity: although still forming filaments, they did not aggregate into the highly condensed depositions that are typical for amyloid. In addition, they could be solubilized in 200 mM-NaCl and KCl. When mixed with beta A4 peptides bearing the natural sequence, two of the analogues could inhibit the formation of filaments in vitro. These results demonstrate that a well-preserved hydrophobic core around residues 17 to 20 of beta A4 is crucial for the formation of beta-sheet structure and the amyloid properties of beta A4. The introduction of structural alterations within this region may guide the development of reagents for the therapy of Alzheimer's disease. 相似文献