全文获取类型
收费全文 | 12271篇 |
免费 | 890篇 |
国内免费 | 8篇 |
出版年
2021年 | 121篇 |
2020年 | 94篇 |
2019年 | 124篇 |
2018年 | 151篇 |
2017年 | 158篇 |
2016年 | 216篇 |
2015年 | 369篇 |
2014年 | 368篇 |
2013年 | 555篇 |
2012年 | 684篇 |
2011年 | 599篇 |
2010年 | 461篇 |
2009年 | 372篇 |
2008年 | 547篇 |
2007年 | 546篇 |
2006年 | 545篇 |
2005年 | 551篇 |
2004年 | 541篇 |
2003年 | 558篇 |
2002年 | 537篇 |
2001年 | 132篇 |
2000年 | 99篇 |
1999年 | 137篇 |
1998年 | 169篇 |
1997年 | 154篇 |
1996年 | 145篇 |
1995年 | 156篇 |
1994年 | 128篇 |
1993年 | 161篇 |
1992年 | 113篇 |
1991年 | 138篇 |
1990年 | 121篇 |
1989年 | 103篇 |
1988年 | 122篇 |
1987年 | 108篇 |
1986年 | 91篇 |
1985年 | 111篇 |
1984年 | 172篇 |
1983年 | 141篇 |
1982年 | 140篇 |
1981年 | 151篇 |
1980年 | 125篇 |
1979年 | 110篇 |
1978年 | 131篇 |
1977年 | 101篇 |
1976年 | 87篇 |
1975年 | 94篇 |
1974年 | 80篇 |
1973年 | 67篇 |
1970年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
Elena I. Mikhailova Tomás Naranjo Ken Shepherd Jannie Wennekes-van Eden Christa Heyting J. Hans de Jong 《Chromosoma》1998,107(5):339-350
The Ph1 locus in wheat influences homo(eo)logous chromosome pairing. We have analysed its effect on the behaviour and morphology
of two 5RL rye telosomes in a wheat background, by genomic in situ hybridisation (GISH), using rye genomic DNA as a probe.
Our main objective was to study the effect of different alleles of the Ph1 locus on the morphology and behaviour of the rye telosomes in interphase nuclei of tapetal cells and in pollen mother cells
at early stages of meiosis. The telosomes, easily detectable at all stages, showed a brightly fluorescing chromomere in the
distal region and a constriction in the proximal part. These diagnostic markers enabled us to define the centromere and telomere
regions of the rye telosomes. In the presence of functional copies of Ph1, the rye telosomes associated at pre-leptotene, disjoined and reorganised their shape at leptotene, and became fully homologously
paired at zygotene – pachytene. In plants without functional alleles (ph1bph1b), the rye telosomes displayed an aberrant morphology, their premeiotic associations were clearly disturbed and their pairing
during zygotene and pachytene was reduced and irregular. The Ph1 locus also influenced the behaviour of rye telosomes in the interphase nuclei of tapetal cells: in Ph1Ph1 plants, the rye telosomes occupied distinct, parallel-oriented domains, whereas in tapetal nuclei of ph1bph1b plants they were intermingled with wheat chromosomes and showed a heavily distorted morphology. The results shed new light
on the effect of Ph1, and suggest that this locus is involved in chromosome condensation and/or scaffold organisation. Our explanation might account
for various apparently contradictory and pleiotropic effects of this locus on both premeiotic associations of homologues,
the regulation of meiotic homo(eo)logous chromosome pairing and synapsis, the resolution of bivalent interlockings and centromere
behaviour.
Received: 27 April 1998; in revised form: 5 August 1998 / Accepted: 11 August 1998 相似文献
992.
Intracellular Glucose Concentration in Derepressed Yeast Cells Consuming Glucose Is High Enough To Reduce the Glucose Transport Rate by 50%
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bas Teusink Jasper A. Diderich Hans V. Westerhoff Karel van Dam Michael C. Walsh 《Journal of bacteriology》1998,180(3):556-562
In Saccharomyces cerevisiae cells exhibiting high-affinity glucose transport, the glucose consumption rate at extracellular concentrations above 10 mM was only half of the zero trans-influx rate. To determine if this regulation of glucose transport might be a consequence of intracellular free glucose we developed a new method to measure intracellular glucose concentrations in cells metabolizing glucose, which compares glucose stereoisomers to correct for adhering glucose. The intracellular glucose concentration was 1.5 mM, much higher than in most earlier reports. We show that for the simplest model of a glucose carrier, this concentration is sufficient to reduce the glucose influx by 50%. We conclude that intracellular glucose is the most likely candidate for the observed regulation of glucose import and hence glycolysis. We discuss the possibility that intracellular glucose functions as a primary signal molecule in these cells. 相似文献
993.
Agrin Can Mediate Acetylcholine Receptor Gene Expression in Muscle by Aggregation of Muscle-derived Neuregulins 总被引:7,自引:1,他引:6
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
994.
Pure phloem sap of tomato leaves was collected by stylectomy.Glutamine and glutamate were the predominant free amino acidstranslocated by the phloem stream. In developing fruits glutaminecontent increased significantly, reaching 35% of the total freeamino acids. Comparison in the amino acid composition betweenthe two tissues are discussed. (Received October 6, 1997; Accepted January 27, 1998) 相似文献
995.
996.
Peter Seiler Ulrich Kalinke Thomas Rülicke Etienne M. Bucher Christian B?se Rolf M. Zinkernagel Hans Hengartner 《Journal of virology》1998,72(3):2253-2258
Following infection of mice with lymphocytic choriomeningitis virus (LCMV), virus-neutralizing antibodies appear late, after 30 to 60 days. Such neutralizing antibodies play an important role in protection against reinfection. To analyze whether a neutralizing antibody response which developed earlier could contribute to LCMV clearance during the acute phase of infection, we generated transgenic mice expressing LCMV-neutralizing antibodies. Transgenic mice expressing the immunoglobulin μ heavy chain of the LCMV-neutralizing monoclonal antibody KL25 (H25 transgenic mice) mounted LCMV-neutralizing immunoglobulin M (IgM) serum titers within 8 days after infection. This early inducible LCMV-neutralizing antibody response significantly improved the host’s capacity to clear the infection and did not cause an enhancement of disease after intracerebral (i.c.) LCMV infection. In contrast, mice which had been passively administered LCMV-neutralizing antibodies and transgenic mice exhibiting spontaneous LCMV-neutralizing IgM serum titers (HL25 transgenic mice expressing the immunoglobulin μ heavy and the κ light chain) showed an enhancement of disease after i.c. LCMV infection. Thus, early-inducible LCMV-neutralizing antibodies can contribute to viral clearance in the acute phase of the infection and do not cause antibody-dependent enhancement of disease.Against many cytopathic viruses such as poliovirus, influenza virus, rabies virus, and vesicular stomatitis virus, protective virus-neutralizing antibodies are generated early, within 1 week after infection (3, 31, 36, 44, 49). In contrast, several noncytopathic viruses (e.g., human immunodeficiency virus and hepatitis viruses B and C in humans or lymphocytic choriomeningitis virus [LCMV] in mice) elicit poor and delayed virus-neutralizing antibody responses (1, 7, 20, 24, 27, 35, 45, 48).In the mouse, the natural host of LCMV, the acute LCMV infection is predominantly controlled by cytotoxic T lymphocytes (CTLs) in an obligatory perforin-dependent manner (13, 18, 28, 50). In addition to the CTL response, LCMV-specific antibodies are generated. Early after infection (by day 8), a strong antibody response specific for the internal viral nucleoprotein (NP) is mounted (7, 19, 23, 28). These early LCMV NP-specific antibodies exhibit no virus-neutralizing capacity (7, 10). Results from studies of B-cell-depleted mice and B-cell-deficient mice implied that the early LCMV NP-specific antibodies are not involved in the clearance of LCMV (8, 11, 12, 40). Late after infection (between days 30 and day 60), LCMV-neutralizing antibodies develop (7, 19, 22, 28, 33); these antibodies are directed against the surface glycoprotein (GP) of LCMV (9, 10). LCMV-neutralizing antibodies have an important function in protection against reinfection (4, 6, 38, 41, 47).In some viral infections, subprotective virus-neutralizing antibody titers can enhance disease rather than promote host recovery (i.e., exhibit antibody-dependent enhancement of disease [ADE] [14, 15, 21, 46]). For example, neutralizing antibodies are involved in the resolution of a primary dengue virus infection and in the protection against reinfection. However, if subprotective neutralizing antibody titers are present at the time of reinfection, a severe form of the disease (dengue hemorrhagic fever/dengue shock syndrome [15, 21]), which might be caused by Fc receptor-mediated uptake of virus-antibody complexes leading to an enhanced infection of monocytes (15, 16, 25, 39), can develop. Similarly, an enhancement of disease after intracerebral (i.c.) LCMV infection was observed in mice which had been treated with virus-neutralizing antibodies before the virus challenge (6). ADE in LCMV-infected mice was either due to an enhanced infection of monocytes by Fc receptor-mediated uptake of antibody-virus complexes or due to CTL-mediated immunopathology caused by an imbalanced virus spread and CTL response.To analyze whether LCMV-neutralizing antibodies generated early after infection improve the host’s capacity to clear the virus or enhance immunopathological disease, immunoglobulin (Ig)-transgenic mice expressing LCMV-neutralizing IgM antibodies were generated. After LCMV infection of transgenic mice expressing the Ig heavy chain (H25 transgenic mice), LCMV-neutralizing serum antibodies were mounted within 8 days, which significantly improved the host’s capacity to eliminate LCMV. H25 transgenic mice did not show any signs of ADE after i.c. LCMV infection.Transgenic mice expressing the Ig heavy and light chains (HL25 transgenic mice) exhibited spontaneous LCMV-neutralizing serum antibodies and confirmed the protective role of preexisting LCMV-neutralizing antibodies, even though the neutralizing serum antibodies were of the IgM isotype. Similar to mice which had been treated with LCMV-neutralizing antibodies, HL25 transgenic mice developed an enhanced disease after i.c. LCMV infection, which indicated that ADE was due to an imbalance between virus spread and CTL response. Thus, the early-inducible LCMV-neutralizing antibody response significantly enhanced clearance of the acute infection without any risk of causing ADE. 相似文献
997.
The disappearance of spawned copepod eggs can, at times, approach100% day1 and may be a bottleneck to population recruitmentof marine copepods. We examined the egg production rate andegg hatching success of Centropages hamatus and Temora longicomis(Copepoda: Calanoida) on natural diets, and the role of delayedhatching combined with high sinking rates in removing theireggs from the water column. Cumulative hatching success withinIS days was consistently high from March to June 1996: 相似文献
998.
Michaël H. Kolk Sybren S. Wijmenga Hans A. Heus Cornelis W. Hilbers 《Journal of biomolecular NMR》1998,12(3):423-433
The complete T- and pseudoknotted acceptor arm of the tRNA-like structure of turnip yellow mosaic virus (TYMV) genomic RNA has been studied by NMR spectroscopy. Resonance assignment and the gathering of restraints of the 44-mer are impeded by spectral complexity as well as by line broadening. The latter is caused by local dynamical effects in the pseudoknot domain in the molecule. These specific problems could be solved by using different field strengths and selectively 13C/15 labeled samples. Experiments for assigning the sugar spin systems were adjusted to satisfy the requirements of this system. Furthermore, the quality of the structure could be improved by determining the backbone torsion angles , and , using new approaches that were tailored for use in large RNA molecules. 相似文献
999.
Patrik Andersson Bernard Gsell Beat Wipf Hans Senn Gottfried Otting 《Journal of biomolecular NMR》1998,11(3):279-288
An HMQC experiment is proposed, dubbed FHMQC, where water flip-back is achieved by a single water-selective pulse preceding the basic HMQC pulse sequence. The scheme is demonstrated with a 15N, 1H-HMQC spectrum of uniformly 15N/2H-labelled S. aureus DNA gyrase B with a molecular weight of 45 kDa for the unlabelled protein. The sensitivity of the experiment is improved compared to that of an FHSQC spectrum. It is further shown that the original FHSQC experiment can be shortened by the use of bipolar gradients. Relaxation times of different 15N magnetizations and coherences were measured. The new FHMQC scheme is implemented in 3D NOESY-15N-HMQC and 3D15 N-HMQC-NOESY-15N-HMQC pulse sequences which are demonstrated with a 24 kDa fragment of uniformly 15N/13C/2H-labelled S. aureus DNA gyrase B. 相似文献
1000.
Hans Ulrich Stilz Wolfgang Guba Bernd Jablonka Melitta Just Otmar Klingler Wolfgang König Volkmar Wehner Gerhard Zoller 《Letters in Peptide Science》1998,5(2-3):215-221
Antagonists of the platelet fibrinogen receptor (GP IIb/IIIa receptor) are expected to be a new promising class of antithrombotic agents. The binding of fibrinogen to the fibrinogen receptor depends on an Arg-Gly-Asp-Ser (RGDS) tetrapeptide recognition motif. Structural modifications of the RGDS lead have led to the discovery of a non-peptide RGD mimetic GP IIb/IIIa antagonist 20 (S 1197). Compound 20 inhibits dose-dependently and reversibly human platelet aggregation. Modeling studies based on structure–activity data revealed the following structural features of the drug as important for receptor binding: the amidino group, the carboxylate group, hydrophobic substitutions at the carboxyl-terminus and at the side chain carrying the positive charge, the carboxyl-terminal NH group of the -amino acid as a hydrogen bond donor and one oxygen atom of the hydantoin as a hydrogen bond acceptor. The ethyl ester prodrug of 20 (S 5740) is an orally active antithrombotic agent which has the potential to be used to treat and prevent thrombotic diseases in humans. 相似文献