全文获取类型
收费全文 | 63454篇 |
免费 | 5359篇 |
国内免费 | 30篇 |
出版年
2022年 | 426篇 |
2021年 | 892篇 |
2020年 | 552篇 |
2019年 | 665篇 |
2018年 | 864篇 |
2017年 | 804篇 |
2016年 | 1421篇 |
2015年 | 2493篇 |
2014年 | 2609篇 |
2013年 | 3454篇 |
2012年 | 4374篇 |
2011年 | 4400篇 |
2010年 | 2851篇 |
2009年 | 2510篇 |
2008年 | 3643篇 |
2007年 | 3717篇 |
2006年 | 3493篇 |
2005年 | 3525篇 |
2004年 | 3451篇 |
2003年 | 3261篇 |
2002年 | 3258篇 |
2001年 | 835篇 |
2000年 | 647篇 |
1999年 | 819篇 |
1998年 | 924篇 |
1997年 | 653篇 |
1996年 | 648篇 |
1995年 | 629篇 |
1994年 | 604篇 |
1993年 | 629篇 |
1992年 | 608篇 |
1991年 | 537篇 |
1990年 | 437篇 |
1989年 | 460篇 |
1988年 | 446篇 |
1987年 | 392篇 |
1986年 | 373篇 |
1985年 | 441篇 |
1984年 | 481篇 |
1983年 | 402篇 |
1982年 | 485篇 |
1981年 | 442篇 |
1980年 | 399篇 |
1979年 | 271篇 |
1978年 | 327篇 |
1977年 | 315篇 |
1976年 | 256篇 |
1975年 | 256篇 |
1974年 | 274篇 |
1973年 | 248篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
991.
Peter J. M. Hendriksen Marion Tieman Tette Van Der Lende Lawrence A. Johnson 《Molecular reproduction and development》1993,35(2):189-196
Studies designed to answer the question whether or not H-Y antigen is preferentially expressed on Y chromosome bearing sperm have resulted in conflicting results. This is probably due to the absence of reliable methods for estimating the percentage of X and Y chromosome bearing sperm in fractions, enriched or depleted for H-Y antigen positive sperm. In recent years a reliable method for separating X and Y chromosome bearing sperm has been published. With this method, separation is achieved by using a flow cytometer/cell sorter, which detects differences in DNA content. This technique provided the first opportunity for testing anti-H-Y antibody binding to fractions enriched for X and Y chromosme bearing sperm, directly. A total of 7 anti-H-Y monoclonal antibodies were tested using sorted porcine sperm and in one experiment also sorted bovine sperm. All monoclonal antibodies bound only a fraction of the sperm (20 to 50%). However, no difference in binding to the X and Y sperm enriched fractions was found. Therefore, the present experiments do not yield evidence that H-Y antigen is preferentially expressed in Y chromosome bearing sperm. © 1993 Wiley-Liss, Inc. 相似文献
992.
Lasse T. Keetz Eva Lieungh Kaveh Karimi-Asli Sonya R. Geange Emiliano Gelati Hui Tang Yeliz A. Yilmaz Kjetil S. Aas Inge H. J. Althuizen Anders Bryn Stefanie Falk Rosie Fisher Anne Fouilloux Peter Horvath Sunniva Indrehus Hanna Lee Danica Lombardozzi Frans-Jan W. Parmentier Norbert Pirk Vigdis Vandvik Ane V. Vollsnes Olav Skarpaas Frode Stordal Lena M. Tallaksen 《Global Change Biology》2023,29(15):4440-4452
Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines. 相似文献
993.
The aim of this study was to delineate the flow patterns in a non-unidirectional flow field inside a ventricle-shaped cell
culture chamber, and examine the resulting morphology and integrity of the endothelium in select regions of the monolayer.
The chamber was perfused by pulsatile flow, and the coherent motion of the fluid was studied using flow visualization aided
by image analysis. Four distinct flow patterns were discerned and examined: central jet, flow impingement, flow separation,
and recirculating eddies. The influence of these patterns on endothelial cell morphology was assessed after 20 h of exposure
to flow. There were no signs of damage to the endothelium in the jet region nor was there evidence of cell alignment with
the flow. Yet, there were changes in cell morphology and cytoskeletal architecture as compared to control. By contrast, within
the eddies where the flow was highly disturbed, there was apparent damage to the endothelium. Thus, exposure of cells to random
velocity fluctuations in regions of quasi-static flow compromises the integrity of the monolayer. Identification of such sites
and acquisition of the knowledge necessary to protect the cells from denudation will be valuable for the endothelialization
efforts of cardiac prostheses. 相似文献
994.
Terje Kalland Mikael Dohlsten Lars Abrahmsén Gunnar Hedlund Per Björk Peter A. Lando Anette Sundstedt Eva Åkerblom Peter Lind 《Cell biochemistry and biophysics》1993,22(1-3):147-164
The bacterial superantigen staphylococcal enterotoxin A (SEA) is an extremely potent activator of T lymphocytes when presented on MHC class II antigens. In order to induce T lymphocytes to reject a tumor, we substituted the specificity of SEA for MHC class II molecules with specificity for tumor cells by combining SEA with a MAb recognizing colon carcinomas. Chemical conjugates or recombinant fusion proteins of the MAb C215 and SEA retained excellent antigen binding properties whereas the binding to MHC class II was markedly reduced. The hybrid proteins directed SEA responsive T cells to tumors with specificity determined by the specificity of the MAb. Significant tumor cell killing was obtained at picomolar concentrations of the hybrid proteins and was the result of direct cell mediated by cytotoxicity as well as production of tumoricidal cytokines by T cells. Targeting of superantigens represents a novel approach to specific immunomodulation and deserves further study as a potential therapy for malignant disease. 相似文献
995.
Peter R. Bieck Karl-Heinz Antonin Gisbert Farger Erik B. Nilsson Eckhart K. Schmidt Philippe Dostert Margherita Strolin Benedetti Peter C. Waldmeier 《Neurochemical research》1993,18(11):1163-1167
CGP 28 014 is a specific inhibitor of catechol-O-methyltransferase (COMT) in vivo. In humans, the inhibition was assessed by measuring urinary excretion of isoquinolines and with the levodopa test. Following administration of CGP 28 014, urinary excretion of isoquinolines was significantly increased. In rats, CGP 28 014 reduced plasma and striatal concentrations of 3-O-methyldopa (30MD) in a dose-dependent manner. Acute and subchronic administration of CGP 28 014 alone or in combination with the peripherally acting decarboxylase inhibitor benserazide decreased plasma 30MD as an index of COMT inhibition by about 50%. There seems to be a close relationship between the time-course of plasma concentrations of CGP 28 014 and the extent of COMT inhibition assessed by the 30MD/DOPA ratio in plasma. 相似文献
996.
SruI restriction endonuclease from Selenomonas ruminantium 总被引:1,自引:0,他引:1
Ivan Vanat Peter Prista Elena Ryboovál rej Godány Peter Javorský 《FEMS microbiology letters》1993,113(2):129-132
Abstract Sru I, specific restriction endonuclease, has been characterized from Selenomonas ruminantium isolated from the rumen of fallow deer. Results from the study demonstrate that S. ruminantium 18D possesses a type II restriction endonuclease, which recognizes the sequence 5'-TTT↓AAA-3'. The recognition sequence of Sru I was identified using digestions on pBR322, pBR328, pUC18, M13mp18RF, pACYC184 and λDNA. The cleavage patterns obtained were compared with computer-derived data. Sru I recognises the palindromic hexanucleotide sequence and cleaves DNA after the third T in the sequence, producing blunt ends. The purification and characterization of restriction endonuclease Sru I presented here is the first described for Selenomonas ruminantium spp. and demonstrates that this microorganism pocesses a DNA-cleaving enzyme with the same specificity as Dra I or Aha III. 相似文献
997.
Jörg Schmid Peter Möller Gerd Moldenhauer Bernd Dörken Heiner Bihl Siegfried Matzku 《Cancer immunology, immunotherapy : CII》1993,36(4):274-280
Accumulation of radiolabelled monoclonal antibodies (mAb) in human B-lymphoma xenografts was found to result in two distinct patterns. The basic elements leading to these patterns were elucidated by autoradiographic and immunohistological analysis applied to the nude mouse xenografts BJAB and OCI.LY1. With BJAB, accumulation occurred exclusively in peripheral cell layers of the lymphoma nodule, while central areas were not accessible irrespective of mAb dose. This feature was the consequence of an inefficient transport across intratumoral vessels together with peripheral mAb supply through a subcapsular pseudosinus. With OCI.LY1, intratumoral vessels showed generalized leakiness. Furthermore, interstitial transport was operative to a fair extent, such that in early images multiple sites of mAb extravasation were obvious, which coalesced during the course of prolonged uptake. The pattern of peripheral mAb uptake resulted in a low overall tumour uptake, while multifocal uptake yielded substantial accumulation values. 相似文献
998.
999.
A PCR primer-specific to Cylindrocarpon heteronema for detection of the pathogen in apple wood 总被引:1,自引:0,他引:1
Averil E. Brown S. Muthumeenakshi S. Sreenivasaprasad Peter R. Mills Terence R. Swinburne 《FEMS microbiology letters》1993,108(1):117-120
Abstract An oligonucleotide primer (ChInt) was synthesised from the variable internally transcribed spacer (ITS) 1 region of ribosomal DNA (rDNA) of Cylindrocarpon heteronema . PCR with primers ChInt and ITS4 (from a conserved sequence of the rDNA) amplified a 470-bp fragment from several isolates of C. heteronema but not from various apple wood saprophytes. Amplification of this fragment was achieved from 1–2 pg of fungal DNA. These primers amplified a fragment of the same size from DNA extracted from cankered wood but only after impurities were removed from the DNA on a Qiagen tip-5 column. Southern hybridization analysis confirmed the 470-bp fragment from C. heteronema DNA and cankered wood to be identical. 相似文献
1000.
Inhibition of Bordetella pertussis filamentous hemagglutinin-mediated cell adherence with monoclonal antibodies 总被引:6,自引:0,他引:6
Elizabeth Leininger Peter G. Probst Michael J. Brennan James G. Kenimer 《FEMS microbiology letters》1993,106(1):31-38
Abstract Filamentous hemagglutinin (FHA), a 220-kDa protein located on the surface of Bordetella pertussis , is one of the major cell adhesins of this bacterium. We have produced three hybridoma cell lines that express monoclonal antibodies (mAbs) against FHA: X3C, X3E and X4B. The anti-FHA mAbs X3C and X3E reacted with 220-kDa FHA protein bands on Western blots. The mAb X4B, which reacted with FHA in ELISA, did not bind to FHA in a Western blot assay. All three mAbs seemed to be directed to the same epitope or to epitopes in close proximity as suggested by competition ELISAs. All three mAbs were able to inhibit the adherence of Chinese hamster ovary cells to purified FHA, and they could also inhibit the FHA-mediated agglutination of goose red blood cells. The attachment of B. pertussis to epithelial cell monolayers was inhibited by the mAb X3C. These antibodies are very useful probes to identify the presence of FHA in bordetellae species and in clinical reagents such as pertussis vaccines, and to characterize the functional domains of this important bacterial adhesin. 相似文献