全文获取类型
收费全文 | 6808篇 |
免费 | 488篇 |
出版年
2018年 | 82篇 |
2017年 | 88篇 |
2016年 | 141篇 |
2015年 | 230篇 |
2014年 | 285篇 |
2013年 | 289篇 |
2012年 | 396篇 |
2011年 | 421篇 |
2010年 | 268篇 |
2009年 | 191篇 |
2008年 | 322篇 |
2007年 | 308篇 |
2006年 | 275篇 |
2005年 | 287篇 |
2004年 | 271篇 |
2003年 | 241篇 |
2002年 | 248篇 |
2001年 | 210篇 |
2000年 | 264篇 |
1999年 | 180篇 |
1998年 | 70篇 |
1997年 | 53篇 |
1996年 | 64篇 |
1995年 | 56篇 |
1994年 | 59篇 |
1993年 | 51篇 |
1992年 | 117篇 |
1991年 | 125篇 |
1990年 | 118篇 |
1989年 | 78篇 |
1988年 | 108篇 |
1987年 | 83篇 |
1986年 | 79篇 |
1985年 | 82篇 |
1984年 | 78篇 |
1983年 | 58篇 |
1982年 | 59篇 |
1981年 | 48篇 |
1980年 | 41篇 |
1979年 | 75篇 |
1978年 | 44篇 |
1977年 | 57篇 |
1976年 | 35篇 |
1975年 | 53篇 |
1974年 | 38篇 |
1973年 | 52篇 |
1972年 | 39篇 |
1971年 | 43篇 |
1969年 | 37篇 |
1968年 | 36篇 |
排序方式: 共有7296条查询结果,搜索用时 62 毫秒
171.
D. W. Dunham H. Schöne 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1984,154(4):511-513
Summary
Coenobita clypeatus were tested on an underwater inclined plane in order to determine their behavioral threshold for perceiving slope, and to investigate the relative importance of input from the statocyst organ and from the weight of the body and gastropod shell on upward orienting ability. The shell's weight was compensated for by a neutral float and increased by weights. The crabs perceive an inclination of less than 5°, and do so with increasing certainty as the slope increases. Perception of the slope seems to be both by statocyst and proprioceptive input, but the latter is not essential for upward orientation. 相似文献
172.
Electron microscopic demonstration of calcitonin in human medullary carcinoma of thyroid by the immuno gold staining method 总被引:1,自引:0,他引:1
In a human medullary carcinoma of thyroid gland containing calcitonin in light microscopic demonstration by the avidin biotin complex (ABC) method characteristic secretory granules were found electron microscopically in the cytoplasm of the tumour cells. They consisted in so-called type I granules (270 +/- 25 nm) and type II granules (135 +/- 17 nm). By the immuno gold staining (IGS) method the content of many secretory granules measuring 85-270 nm (152 +/- 18 nm) in diameter could be identified as calcitonin. These granules seemed to be predominantly of type II because of their nearly corresponding size and feature. The type I granules were less frequent in number and they showed no or little immunoreactivity. The results indicate that the IGS-method is practicable to demonstrate the ultrastructural localization of calcitonin and to identify clearly the nature of intracytoplasmic granules in electron microscopy. 相似文献
173.
Schönheit Peter Beimborn Dieter B. Perski Hans-Joachim 《Archives of microbiology》1984,140(2-3):247-251
Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K+]intracellular/[K+]extracellular) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (14C) tetraphenylphosphonium (TPP+). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of 12C-TTP+ (2 mol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed.These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K+ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.Non-common abbreviations TPP+
Tetra phenylphosphonium bromide
- DTE
Dithioerythritol
- TCS
3,5,3,4-Tetrachlorosalycylanilide 相似文献
174.
B Wilke H Jahr S Schmidt H Sch?fer D Gottschling H Fiedler H Zühlke 《Endokrinologie》1977,69(2):233-238
By feeding a regular laboratory chow, sand rats (Psammomys obesus) from our breeding colony gained different body weights, though they received approximately the same quantity of calories. Sand rats, reaching a body weight above 160 g (group B) showed significantly increased blood glucose values in contrast to the animals with a body weight under 160 g (group A). Isolated pancreatic islets of these two groups of sand rats were incubated with [3H]-leucine to study the incorporation of this amino acid into proinsulin and insulin. The incorporation into proteins of pancreatic islets of sand rats of group B was stimulated by 0.45 mg and 3.0 mg/ml glucose. In group A there was no further stimulation from 0.45 mg to 3.0 mg/ml glucose. Insulin secretion could be stimulated by glucose in both groups, but the stimulation was stronger in group B than in group A. 相似文献
175.
Hartmut Land Klaus P. Schäfer 《Biochemical and biophysical research communications》1977,79(3):947-957
Nuclei from Concanavalin A-stimulated lymphocytes (30 hr after Con A addition) incorporate up to 5 times more (3-H)UTP into RNA than nuclei from resting lymphocytes. The incorporation kinetics is linear for almost 60 min. 14–20% of the labeled RNA is polyadenylated. Poly(A) (?)RNA from both types of nuclei sediments from 4–5S up to more than 30S on sucrose gradients. Nuclei from stimulated cells synthesize about double the amount of RNA larger than 18S than nuclei from resting cells. The same holds for poly(A) (+)RNA. Poly(A) (?) RNA labeled during 10 min in both types of nuclei is stable during a 30 min chase. Under the same conditions poly(A) (+)RNA in nuclei from resting cells is degraded to about 50% during the chase whereas it is stable in nuclei from stimulated cells. 相似文献
176.
Role of carbohydrate in biological functions of Friend murine leukemia virus gp71. 总被引:5,自引:4,他引:1 下载免费PDF全文
Purified gp71 of Friend murine leukemia virus (FLV) can interfere with virus infection, absorb neutralizing antibody, and in the presence of group-specific anti-gp71 antibody, hemagglutinate sheep erythrocytes. Interference by FLV gp71 with several murine leukemia viruses (MuLV) was tested in the XC and S + L- assay systems. Treatment of gp71 with trypsin or Pronase eliminated its interfering capacity. However, treatment with neuraminidase or a mixture of glycosidase enzymes, which left the major serological properties of gp71 intact, did not reduce the interference potential of gp71 for FLV or AKR MuLV. The capacity of gp71 to absorb type- or group-specific virus-neutralizing antibodies was similarly affected by the various enzyme treatments. In contrast, indirect hemagglutination by gp71 was abolished not only by proteases but also by treatment with glycosidase enzymes, although neuraminidase had no effect. Preliminary data indicate that infectivity of FLV or xenotropic MuLV was not affected by short treatment with glycosidase enzymes. 相似文献
177.
The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of Pfr, the far-red light absorbing form of phytochrome (e.g., by [Pfr]0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by Pfr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to Pfr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by Pfr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of Pfr established at the onset of darkness rather than by the actual Pfr level present during the growth period.Abbreviation Pfr
far-red light absorbing form of phytochrome 相似文献
178.
The water permeability of periderm membranes stripped from mature trees of Betula pendula Roth was investigated. The diffusion of water was studied using the system water/membrane/water, and transpiration was measured using the system water/membrane/water vapor. Betula periderm consists of successive periderm layers each made up of about 5 heavily suberized cell layers and a varying number of cell layers that are little suberized, if at all. It is shown that these layers act as resistances in series. The permeability coefficient of the diffusion of water (P
d) can be predicted with 79% accuracy from the reciprocal of the membrane weight (x in mg cm-2) by means of the linear equation P
d=14.69·10-7
x-0.73·10-7. For example, the P
d of a periderm membrane having a weight of 10 mg cm-2 (approx. 250 m thick) is 7.4·10-8 cm s-1, which is comparable to the permeability of cuticles. This comparison shows that on a basis of unit thickness, Betula periderm is quite permeable to water as cuticles have the same resistance with a thickness of only 0.5 to 3 m. It is argued that this comparatively high water permeability of birch periderm is due to the fact that middle lamellae and the primary walls of periderm cells are not at all, or only incompletely suberized and, therefore, form a hydrophilic network within which the water can flow. This conclusion is based on the following observations: (1) Middle lamellae and primary walls stain strongly with toluidine blue, which shows them to be polar. (2) If silver ions are added as tracer for the flow of water, they are found only in the middle lamellae, primary walls, and in plasmodesmata, while no silver can be detected in the suberized walls. (3) Permeability coefficients of transpiration strongly depend on water activity. This shows conclusively that water flows across Betula periderm via a polar pathway. It is further argued that liquid continuity is likely to be maintained under all physiological conditions in the network formed by middle lamellae and primary walls. On the other hand, the lumina of periderm cells, intercellular air spaces in the lenticels, and even the pores in the suberized walls (remainders of plasmodesmata) will drain at a humidity of 95% and below. Due to the presence of intercellulars the permeability coefficient of lenticels is much greater than that of the periderm. A substantial amount of the total water, therefore, flows as vapor through lenticels even though they cover only 3% of the surface.Abbreviations PM
perideron membrane
-
P
d
permeability coefficient for diffusion of water
-
P
tt
permeability coefficient of transpiration
- MES
(N-morpholino)ethane sulfonic acid 相似文献
179.
Following oral administration of 9,11- 3H-17α-cyano-methylestra-1,3,5(10)-triene-3,17-diol 3-methyl ether, urinary metabolites were studied in man, baboon, beagle dog, minipig and rat. The metabolite pattern revealed remarkable species differences, especially in quantitative respects. 17α-Cyanomethylestra-1,3,5(10)-triene-3,17-diol, 17α-cyanomethylestra-1,3,5(10)-triene-2,3,17-triol 2-methyl ether, 17α-hydroxymethylestra-1,3,5(10)-triene-3,17-diol and 17α-cyanomethylestra-1,3,5(10)-triene-3,16,17-triol were isolated as principal metabolites. In rat bile, a metabolite was tentatively identified as aγ-lactone of a 17α-carbozymethyl-16α-hydroxy compound. 相似文献
180.
Dr. Karen S. Zier Bernd Gänsbacher Sigfried Scholz Ekkehard D. Albert 《Immunogenetics》1980,10(5):513-520
The primed lymphocyte typing test (PLT) is used to detect the gene products of theHLA-D region which are responsible for secondary restimulation of cells primed in MLC. Alternatively, products of theHLA-D region may be detected serologically using antisera directed against a subpopulation of lymphocytes; these are the so-called DRw determinants. The PLT was used to see if it were possible to detect heterogeneity within a given serologically defined group using a cellular test. As priming combinations, we used family members identical for one haplotype and differing in theHLA-A, B andC regions, but not theD region of the second haplotype. Our results indicated that it was possible to prime against this second haplotype and that the segregation of the difference followedHLA. Therefore, using a cellular test it was possible to detect differences among cells belonging to a given DRw group. This suggests that PLT can be a useful tool to identify those serological groups which are composed of heterogenous determinants. In addition, it points out the problem in using any one test to establish identity of theHLA-D region, especially for clinical purposes. 相似文献