全文获取类型
收费全文 | 6727篇 |
免费 | 542篇 |
国内免费 | 3篇 |
出版年
2022年 | 32篇 |
2021年 | 69篇 |
2020年 | 61篇 |
2019年 | 54篇 |
2018年 | 98篇 |
2017年 | 79篇 |
2016年 | 131篇 |
2015年 | 244篇 |
2014年 | 277篇 |
2013年 | 318篇 |
2012年 | 464篇 |
2011年 | 405篇 |
2010年 | 281篇 |
2009年 | 233篇 |
2008年 | 368篇 |
2007年 | 390篇 |
2006年 | 361篇 |
2005年 | 349篇 |
2004年 | 329篇 |
2003年 | 325篇 |
2002年 | 319篇 |
2001年 | 103篇 |
2000年 | 81篇 |
1999年 | 95篇 |
1998年 | 109篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 84篇 |
1994年 | 84篇 |
1993年 | 80篇 |
1992年 | 68篇 |
1991年 | 67篇 |
1990年 | 67篇 |
1989年 | 52篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 51篇 |
1985年 | 55篇 |
1984年 | 66篇 |
1983年 | 48篇 |
1982年 | 48篇 |
1981年 | 45篇 |
1980年 | 49篇 |
1979年 | 44篇 |
1978年 | 40篇 |
1977年 | 38篇 |
1974年 | 41篇 |
1972年 | 37篇 |
1970年 | 30篇 |
1969年 | 35篇 |
排序方式: 共有7272条查询结果,搜索用时 390 毫秒
61.
Cells subjected to the events occurring before, during, and after freezing and thawing are exposed to major changes in the
osmotic pressure of the surrounding medium; i.e., the osmolalities can exceed 30. An important question in understanding the
mechanisms of injury is whether cells respond as ideal osmometers to these strongly anisotonic solutions. Mouse and bovine
embryos from eight-cell to blastocyst stage were used to investigate the question. They were found to behave as ideal osmometers
at room temperature over a wide range of tonicities; i.e., from four times isotonic to almost 1/3 times isotonic, ideality
being defined by a Boyle-van't Hoff equation. Embryo volumes increased from 40 to 200% of isotonic over this range and survivals
of mouse embryos were unaffected. However, outside this range the membrane apparently becomes leaky and the survival of mouse
embryos drops sharply. Osmolalities rise to high values during freezing and the paper develops the thermodynamic equations
to show how computed cell volumes as a function of subzero temperature can be translated into the Boyle-van't Hoff format
of cell volume as a function of the reciprocal of osmolality. 相似文献
62.
63.
Activities of membrane-associated phospholipases A1 and A2, and membrane-associated as well as soluble lysophospholipases were measured in different subcellular fractions of rat liver, using suspensions of stereospecifically labelled radioactive phospholipids as substrates. Plasma membranes and endoplasmic reticulum were shown to contain phospholipase A1 and lysophospholipase activities, both of which could be stimulated by Ca2+, mitochondria Ca2+-dependent phospholipase A2 and cytosol Ca2+-independent lysophospholipase activities. Each of these lipolytic enzymes could be inhibited by antimalarial drugs (chloroquine, mepacrine, primaquine) at concentrations above 1 x 10(-4) M. Inhibition of the alkaline cytosolic lysophospholipase by these drugs was noncompetitive with respect to the substrate, and the inhibitory potency increased, when the pH was raised. 相似文献
64.
Vitamin K-dependent carboxylase: the carboxylation of exogenous substrates in different systems 总被引:1,自引:0,他引:1
M A de Boer-van den Berg M M Ulrich H C Hemker B A Soute C Vermeer 《Biochimica et biophysica acta》1985,831(1):94-98
Two types of solid-phase carboxylase, SPC-II and SPC-X, have been prepared from the livers of warfarin-treated cows. Their enzymatic activities were compared with substrate-free carboxylase in microsomes from normal cows and substrate-bound carboxylase in microsomes from warfarin-treated cows. A number of exogenous substrates for carboxylase have been purified and tested. We found that large substrates, such as descarboxyprothrombin, are carboxylated only by substrate-free carboxylase and not by the substrate-bound enzyme. No differences in apparent Km values between solid-phase carboxylases II and X were observed. 相似文献
65.
Summary Dysgenic hybrids of Drosophila melanogaster were screened for the induction of mutations in the Y chromosomal fertility genes. Out of 2,417 Y chromosomes analysed 13 male steriles (ms (Y)) were isolated. This high rate of mutation is most probably due to the unusually large physical size of the fertility genes. 相似文献
66.
Ulrich Lehmann 《Pal?ontologische Zeitschrift》1985,59(1-2):99-108
The ink sacs within the living chambers of ammonites as hitherto published seem to be remains of the stomach-crop-complex. Ammonites had no ink sacs. Fossilised remains of gills were found within the living chambers of three ammonoid specimens (generaOphiceras, Hildoceras, Eleganticeras). Their state of preservation is not good enough to identify their numbers. Their shape seems to be not quite dissimilar to that of recentNautilus. Reflections concerning the eyes of ammonites suggest that they were of the pinhole type like those of recentNautilus. 相似文献
67.
Summary The distribution and storage of major elements in acid soils from a spruce and a beech forest was investigated after fertilization of NH4NO3 and KCl followed by Ca and Mg fertilization by 2 liming applications. All fertilizers were applied on top of the soil without mixing. Most of the added Ca and Mg was detected in the humus layer, a significant part of it still in carbonatic form. The effect of liming on mineral soil pH is very low, and was only observed in the 0–10 cm layer. However, base saturation of the mineral soil increased. The storage of C and N of the humus layer was not affected. N fertilization increased the N storage of the soil only under beech, but was followed by heavy NO3-losses with seepage water under spruce. High leaching rates for K were also found in the spruce stand. The amount of K that was not leached increased the pool of exchangeable K in the deeper soil layer. 相似文献
68.
W. Stauber V. Fritz B. Dahlmann F. Gauthier H. Kirschke R. Ulrich 《The Histochemical journal》1985,17(7):787-796
Summary Proteinases and proteinase inhibitors have become suspect in a wide variety of muscle wasting conditions that might be treatable if knowledge of the cellular locale and function of these molecules were known. Fluorescent probes have been useful in the localization of proteinases in muscle samples from human and animal specimens. These include the histochemical localization of proteinases based on the specific fluorescence of hydrolysis product derivatives, but this approach has been limited to the lysosomal proteinases because of the acidic requirements of the trapping reaction of the primary reaction product. Immunohistochemical techniques do not have the same restrictions and a number of lysosomal and nonlysosomal proteinases have been identified in muscle by this means. Unfortunately, they do not yield any information as to the activity of the enzymes. This is an important consideration since the extracellular environment contains a number of proteinase inhibitors, some of which may be internalized by the cell. 相似文献
69.
By use of the pressure-clamp technique, the hydraulic conductivity of the brackish-water alga Lamprothamnium was found to be 5·10-6 cm s-1 bar-1. The dimensions of the internodes are so small that it is possible, for the first time, to measure a complete volume relaxation upon clamping the turgor pressure to a preset value by a feedback control of the pressure probe. As theoretically predicted, the values of the hydraulic conductivity obtained from the initial slope of the volume relaxation induced by the pressure clamp are in agreement (within experimental error) with those obtained from the half-time of the relaxation process. The cell volume also obtained from the analysis of the volume relaxation is the osmotically effective cell volume and is therefore slightly smaller than the value obtained by taking the dimensions of the cell including the cell wall.Abbreviations and symbols Lp
hydraulic conductivity
- P
turgor pressure
- Sv
initial slope of volume relaxion
- T1/2
half-time of volume relaxation
Dedicated to Professor Dr. H. Ziegler on the occasion of his 60th birthday 相似文献
70.
Methanobacterium thermoaggregans is a new thermophilic autotrophic rod-shaped methane producing bacterium. The organism likes to form aggregates during growth and utilizes only H2 and CO2 as substrates. Growth optimum is at 65°C with a doubling time of 3.5 h. Optimal growth occurs at pH-values between 7 and 7.5. The addition of yeast extract to the mineral salt medium stimulates growth. The DNA base composition is 42 mol% G+C. The organism was isolated from mud taken from a cattle pasture. Because of its optimal growth temperature and its tendency to form aggregates the nameMethanobacterium thermoaggregans is suggested.Abbreviations G+C
Guanine+cytosine 相似文献