全文获取类型
收费全文 | 8282篇 |
免费 | 771篇 |
国内免费 | 1084篇 |
出版年
2024年 | 18篇 |
2023年 | 171篇 |
2022年 | 195篇 |
2021年 | 204篇 |
2020年 | 328篇 |
2019年 | 380篇 |
2018年 | 363篇 |
2017年 | 371篇 |
2016年 | 372篇 |
2015年 | 351篇 |
2014年 | 486篇 |
2013年 | 723篇 |
2012年 | 320篇 |
2011年 | 423篇 |
2010年 | 379篇 |
2009年 | 528篇 |
2008年 | 509篇 |
2007年 | 494篇 |
2006年 | 384篇 |
2005年 | 352篇 |
2004年 | 285篇 |
2003年 | 288篇 |
2002年 | 221篇 |
2001年 | 182篇 |
2000年 | 152篇 |
1999年 | 151篇 |
1998年 | 140篇 |
1997年 | 116篇 |
1996年 | 96篇 |
1995年 | 105篇 |
1994年 | 95篇 |
1993年 | 84篇 |
1992年 | 88篇 |
1991年 | 73篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 50篇 |
1987年 | 61篇 |
1986年 | 49篇 |
1985年 | 57篇 |
1984年 | 60篇 |
1983年 | 40篇 |
1982年 | 69篇 |
1981年 | 46篇 |
1980年 | 39篇 |
1979年 | 39篇 |
1978年 | 24篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 875 毫秒
101.
Dominique Le Grand Michel Solsona Renate Rosengarten francois Poumarat 《FEMS microbiology letters》1996,144(2-3):267-275
Abstract The variability of predominant Mycoplasma bovis surface antigens in the presence of specific immune pressure was analyzed in an in vitro assay to determine if M. bovis could escape immune destruction. We have shown that serum antibodies from immunized or experimentally infected calves and monoclonal antibodies which specifically react with previously characterized or as yet undefined major M. bovis membrane surface proteins cause repression of expression or shortening of the target protein, or induce switching to expression of an antigenically distinct variant protein. We have further demonstrated that removal of the inducing antibody results in reversion to the original phenotype. These results suggest that the level of expression and the length of M. bovis surface antigens in the host is modulated by cognate antibodies. According to the surface antigenic variation systems, random selection of preexisting variants resistant to antibody-mediated inhibition or direct regulation of gene expression may be means by which this organism evades host immune defences. 相似文献
102.
N. Telmon D. Rougé J. F. Brugne J. Pujol G. Larrouy L. Arbus 《International Journal of Anthropology》1996,11(1):1-9
Two methods, a visual method based on the appearance of the auricular surface of the ilium and a metric method based on two
dental criteria, were used in conjunction for estimation of skeletal age at death in paleodemographic study of an ancient
cemetery, and were found to be coherent. However, the paleodemographic profiles differed according to sex, indicating a sexual
difference in the evolution of the sacroiliac joint. 相似文献
103.
Obst O. O. Linssen M. C. J. G. Vusse G. J. v. d. Kammermeier H. 《Molecular and cellular biochemistry》1996,163(1):173-180
Marked concentration differences of noradrenaline (NA) between the vascular and the interstitial compartment were detected by sampling interstitial transudate from isolated perfused rat hearts. The ratios of vascular/interstitial concentration amounted to 7.4 to 1.3 depending on the concentration of NA administered (3 × 10–9 to 10–6 M). These concentration differences were abolished by inhibitors of uptake1 desipramine (DMI) I and uptake, (O-methyl-isoprenaline (OMI)). Neuronal uptake, was characterized by a Km of 0.22 mol/l and a Vmax of 370 pmol × min–1 × gWWT–1, extraneuronal uptake2 by a KUPTAKE of = 0.313 min–4.The apparent permeability surface area (P×S)-product calculated from uptake rate and transcapillary concentration difference was significantly decreased by administrating 100 mol/l (NA) in presence of DMI. A presumed endothelial uptake mechanism contributing to catecholamine translocation was investigated in endothelial cells in culture. These cells showed a specific noradrenaline uptake with a Km of 4.35 mol/l and a Vmax of about 75 pmol × min–1 x gWWT–1. Any inhibiton by inhibitors of both of the two noradrenaline uptakes was lacking. The uptake rate of this mechanism is insufficient to contribute to the diffusive conductivity of the capillary wall (P × S-product). We conclude from our investigations on interstitial concentrations of catecholamines and transcapillary concentration differences, that the capillary wall, owing to its metabolic and diffusional characteristics, influences the exchange of catecholamines to a substantial and physiologically relevant extent. 相似文献
104.
The fluxes of NO and NO2 between wheat canopy monoliths and the atmosphere were investigated with the dynamic chamber technique. For this purpose monoliths were dug out at different plant growth stages from a field site, transported to the institute, and placed in an environmental growth chamber. The wheat canopy monoliths were exposed over a period of four days to the average ratios of atmospheric NO2 and NO measured at the field site, i.e. NO2 concentration of about 18 mL L-1 plus NO concentration lower than 0.5 nL L-1. Under these conditions NO emission into the atmosphere and NO2 deposition into canopy monoliths was observed. Both fluxes showed diurnal variation with maximum rates during the light and minimum rates during darkness. NO2 fluxes correlated with soil temperature as well as with light intensity. NO fluxes correlated with soil temperature but not with light intensity. From the investigation performed the diurnal variation of the NO and NO2 compensation points, the maximum rates of NO and NO2 emission, and the total resistances of NO and NO2 fluxes were calculated. Under the assumption that the measured data are representative for the whole vegetation period, annual fluxes of NO and NO2 were estimated. Annual NO emission into the atmosphere amounted to 87 mg N m-2 y-1 (0.87 kg ha-1 y-1), annual NO2 deposition into canopy monoliths amounted to 1273 mg N m-2 y-1 (12.73 kg ha-1 y-1). Apparently, the uptake of atmospheric nitrogen by the wheat field from NO2 deposition is about 15 times higher than the loss of nitrogen from NO emission. It can therefore be assumed that even in rural areas wheat fields are a considerable sink for atmospheric nitrogen. The annual sink strength estimated in the present study is ca. 12 kg N ha-1 y-1. The possible origin of the NO emitted and the fate of atmospheric NO2 taken up by the wheat canopy monoliths are discussed.Preliminary results of this paper were presented at the Joint Workshop COST 611/Working Party 3 and EUROTRAC in Delft, The Netherlands (Ludwig et al., 1991). 相似文献
105.
Margaret Smallwood Edwin A. Yates William G. T. Willats Helen Martin J. Paul Knox 《Planta》1996,198(3):452-459
Arabinogalactan-proteins (AGPs) occurring in suspension-cultured rice (Oryza saliva L.) cells, their conditioned medium and at the rice root apex were investigated using monoclonal antibodies and the AGP-binding -glucosyl Yariv reagent ( GlcY). A monoclonal antibody, LM2, was generated that recognized an acidic carbohydrate epitope common to two soluble AGPs occurring in the conditioned medium of proliferating rice cells, membrane-associated AGPs (rmAGP) in the cultured cells and two AGPs at the rice root apex. In addition, LM2 recognized AGPs secreted by suspensioncultured carrot (Daucus carota L.) cells. The two AGPs of the rice culture medium, srAGP1 and srAGP2, were discriminated by their mobilities during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, reaction with GlcY, the presence of arabinogalactan epitopes and anion-exchange chromatography. The association of rmAGP with the plasma membrane was investigated by Triton-X-114/aqueous partitioning of both microsomal and plasma-membrane preparations and rmAGP was found to partition into the detergent phase, indicating that AGPs are hydrophobic plasma-membrane proteins in rice. This was in contrast to plasma-membrane AGPs of suspension-cultured carrot cells that partitioned into the aqueous phase. At the rice root apex most of the AGP was associated with the microsomal fraction and also partitioned into the detergent phase, although a distinct highmolecular-mass AGP entered the aqueous phase.Abbreviations AGP
arabinogalactan-protein
- GlcY
-glucosyl Yariv reagent
- ELISA
enzyme-linked immunosorbent assay
We gratefully acknowledge support from the Leverhulme Trust, the UK Biotechnology and Biological Sciences Research Council and the Royal Society. 相似文献
106.
ITE Merlewood Land Classification of Great Britain 总被引:7,自引:0,他引:7
R. G. H. Bunce C. J. Barr R. T. Clarke D. C. Howard A. M. J. Lane 《Journal of Biogeography》1996,23(5):625-634
Abstract. The Institute of Terrestrial Ecology (ITE) has classified the 1 km squares in Great Britain (GB) into thirty-two environmental strata, termed land classes, as a basis for ecological survey. The classes have been used in biogeographical studies of the distribution of individual species and species assemblages. The concept behind the technique is that there is an association between the environmental character of land and ecological parameters. The initial classification was based on a sample of squares drawn from a regular grid. The data for the 12121 km squares classified were drawn from published maps; the number of squares was limited by the available computing power. Subsequently the availability of more powerful computers and the need to improve geographical definition have led to the allocation of every 1 km square to its appropriate class. This paper has been written to summarise the principles involved in the development of the system and indicate the range of projects for which it has been used. The extension of the classification from a sample to the complete coverage of GB revealed the importance of the structure and style of data used to produce the classification. The significance of these conclusions for future work is discussed, with particular reference to automated methods of data capture. 相似文献
107.
The influence of mediterranean pine vole (Microtus (Terricola) duodecimcostatus) mound-building activity in two Western Spanish Pyrenees plant communities (Mesobromion erecti and Festucion eskiae-Nardion strictae) were studied. The plants colonizing the gaps in these areas are different in the two cases considered. The plant composition of surrounding plant communities seems to be the main factor in revegetation. Mound-building activity changes the species' relative frequency and life-form spectrum, decreases the monocytyledonous/dicotyledonous ratio and increases diversity by diminishing the presence of dominant plant species.Abbreviations ME
Mesobromion erecti
- FN
Festucion eskiae-Nardion strictae
- (monocots)
Monocotyledonous
- (dicots)
Dicotyledonous 相似文献
108.
乙肝病毒PreSl片段与乙肝表面抗原羧端的融合表达 总被引:4,自引:0,他引:4
我们利用聚合酶链反应法(PCR)得到了编码乙肝病毒肝细胞受体结合位点PreSl(21 ̄47)的基因片段,并将它分别融合到S基因中相应于第175,188和223位氨基酸残基处。所得到的融合基因插入痘苗病毒表达载体pGJP-5后,在哺乳动物细胞CV-1中进行了暂时表达,对融合蛋白的表达、分泌和抗原性的研究表明,3种融合基因均能表达具有S和PreSl双重抗原性的融合蛋白,但融合位点对表达水平和分泌性质有 相似文献
109.
对陆地表层动力学的研究对象、研究内容及其基本理论方法作了阐述,以多学科综合的观点定义了陆地表层系统,包括时空尺度范围的约定、状态变量的选择、物质循环以及外界因子等的讨论;依据物质和能量守恒原理建立了陆地表层系统的非线性控制方程组,表述了各圈层之间物质循环和能量循环过程、反馈关系及其动力学联系;讨论了控制方程组的整体运作功能以及人类活动对陆地表层系统的影响. 相似文献
110.
Ralph Rapley 《Molecular biotechnology》1995,3(2):139-154
The exquisite specificity of monoclonal antibodies (MAb) has long provided the potential for creating new reagents for the
in vivo delivery of therapeutic drugs or toxins to defined cellular target sites or improved methods of diagnosis. However,
many difficulties associated with their production, affinity, specificity, and use in vivo have largely confined their application
to research or in vitro diagnostics. This situation is beginning to change with the recent developments in the applied molecular
techniques that allow the engineering of the genes that encode antibodies rather than the manipulation of the intact antibodies
themselves. Techniques, such as the polymerase chain reaction, have provided essential methods with which to generate and
modify the genetic constituents of antibodies, allow their conjugation to toxins or drugs, provide ways of humanizing murine
antibodies, and allow discrete modular antigen binding components to be produced. More recent developments of in vitro expression
systems and powerful phage surface display technologies will without doubt play a major role in future antibody engineering
and in the successful development of new diagnostic and therapeutic antibody-based reagents. 相似文献