全文获取类型
收费全文 | 69992篇 |
免费 | 2881篇 |
国内免费 | 1911篇 |
出版年
2023年 | 654篇 |
2022年 | 842篇 |
2021年 | 2123篇 |
2020年 | 1252篇 |
2019年 | 1657篇 |
2018年 | 1351篇 |
2017年 | 979篇 |
2016年 | 1568篇 |
2015年 | 3479篇 |
2014年 | 6806篇 |
2013年 | 6274篇 |
2012年 | 4921篇 |
2011年 | 5569篇 |
2010年 | 3923篇 |
2009年 | 3394篇 |
2008年 | 3500篇 |
2007年 | 3812篇 |
2006年 | 2435篇 |
2005年 | 2069篇 |
2004年 | 1294篇 |
2003年 | 1081篇 |
2002年 | 920篇 |
2001年 | 657篇 |
2000年 | 579篇 |
1999年 | 597篇 |
1998年 | 557篇 |
1997年 | 440篇 |
1996年 | 497篇 |
1995年 | 621篇 |
1994年 | 529篇 |
1993年 | 583篇 |
1992年 | 523篇 |
1991年 | 552篇 |
1990年 | 458篇 |
1989年 | 469篇 |
1988年 | 468篇 |
1987年 | 378篇 |
1986年 | 351篇 |
1985年 | 589篇 |
1984年 | 883篇 |
1983年 | 571篇 |
1982年 | 753篇 |
1981年 | 733篇 |
1980年 | 539篇 |
1979年 | 526篇 |
1978年 | 330篇 |
1977年 | 340篇 |
1976年 | 312篇 |
1974年 | 226篇 |
1973年 | 230篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
91.
Gary L Bratthauer Markku Miettinen Fattaneh A Tavassoli 《The journal of histochemistry and cytochemistry》2003,51(11):1527-1531
Eighteen commercially available antibodies reactive against different cytokeratin proteins were tested on classic examples of lobular intraepithelial neoplasia (LIN) and of ductal intraepithelial neoplasia (DIN) of the breast. About 90% of higher-grade DIN (AIDH and DCIS) show no or substantially diminished reaction with clone 34betaE12 (specified as reactive against keratins 1, 5, 10, and 14 as determined by the manufacturer), while the cells of LIN were found to express the antigen reactive with this antibody. To determine which of these four keratins are present in the cells of LIN, antibodies reactive against these individual four keratins were tested. None of the four antibodies to keratins 1, 5, 10, or 14 reacted with the cells of LIN. To investigate this further, 13 additional monoclonal antibodies to various other keratin proteins were tested on the cells of LIN. Those that successfully reacted with the cells of LIN were further tested on the cells of DIN. All of the individual antibodies reactive with the cells of LIN were also reactive with the cells of DIN to a degree, with clone RCK108 (reactive against keratin 19) coming the closest to demonstrating the reactivity seen with 34betaE12. We conclude that the reactivity seen in the cells of LIN with 34betaE12 is due to either (a) a crossreaction with keratin 19 that is slightly less prominent than the reaction of the individual clone RCK108, (b) a crossreaction with a keratin protein that was not tested (3, 11, 12), (c) a crossreaction with a protein closely resembling keratin in formalin-fixed, paraffin-embedded tissue, or (d) the detection of a mutated or truncated form of keratin 1, 5, 10, or 14 that cannot be detected by the individual monoclonal antibody. 相似文献
92.
K. Tremetsberger C. König R. Samuel W. Pinsker T. F. Stuessy 《Plant Systematics and Evolution》2002,233(3-4):163-181
Genetic variation in 42 populations throughout the range of Biscutella laevigata L. (Brassicaceae), a morphologically variable central European species, has been investigated by enzyme electrophoresis with
three loci (Amy1, Amy2, and Gpi2). Genetic identities and the Fitch-Margoliash tree suggest differentiation into four regional groups: 1) a northwestern
diploid group (northern France and northern Germany), 2) a northeastern diploid group (southern Germany, Upper Austria, northern
Lower Austria, Poland, and Romania), 3) a central diploid group in southern Lower Austria corresponding to subspecies austriaca, and 4) a southern tetraploid group in Alpine areas of France, Germany, Switzerland, Austria, Italy, and Slovenia corresponding
to subspecies laevigata. Geographically isolated diploid relic populations that are genetically depauperate are found in the NW and NE diploid groups.
On the other hand, the diploid relic subspecies austriaca from the NE Prealps and Alps is highly variable. Subspecies laevigata appears to be a genetical autotetraploid with multiple origins involving several diploid progenitors (the NW diploids, subspecies
austriaca and B. prealpina).
Received April 6, 2001; accepted March 6, 2002 Published online: October 14, 2002
Addresses of the authors: Karin Tremetsberger (e-mail: k.tremetsberger@gmx.net), Christiane K?nig, Rosabelle Samuel, Tod
F. Stuessy, Department of Higher Plant Systematics and Evolution, Institute of Botany, University of Vienna, Rennweg 14, A-1030
Vienna, Austria. Wilhelm Pinsker, Institute of Medical Biology, University of Vienna, Waehringerstra?e 10, A-1090 Vienna,
Austria. 相似文献
93.
94.
The Migadopini are a small tribe of Carabidae with 47 species that occur in South America, Australia, and New Zealand, in the sub-Antarctic areas. In South America, most of the genera inhabit areas related to sub-Antartic Nothofagus forest except two monogeneric genera, the Ecuadorian genus Aquilex Moret and the Pampean genus Rhytidognathus Chaudoir. These two genera are geographically isolated from the remaining five South American genera. New material of Rhytidognathus from the northeast of Buenos Aires province and from Entre Ríos province permits establishing that the previous records of Rhytidognathus ovalis (Dejean) for Argentina were erroneous and that it belongs to a new species. Based on external morphological characters and from male and female genitalia we describe Rhytidognathus platensis as a new species. In this contribution we provide illustrations, keys, habitat characteristics and some biogeographic considerations on the distribution of Rhytidognathus. 相似文献
95.
The past, present and future of childhood malaria mortality in Africa 总被引:11,自引:0,他引:11
During the past few years, there has been a historic series of declarations of renewed commitment to malaria control in Africa. Whether the burden of malaria is increasing in Africa is a moot point. This article attempts to re-construct the evidence for the trends in childhood mortality as a result of Plasmodium falciparum infection over the last century in Africa. 相似文献
96.
Roger Cardinal 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1522):1459-1466
Outsider Art (art brut) is defined as a mode of original artistic expression which thrives on its independence, shunning the public sphere and the art market. Such art can be highly idiosyncratic and secretive, and reflects the individual creator''s attempt to construct a coherent, albeit strange, private world. Certain practitioners of what may be termed autistic art are examined in the light of this definition; their work is considered as evidence not of a medical condition but of an expressive intentionality entirely worthy of the interest of those drawn to the aesthetic experience. 相似文献
97.
The effects of co-evolution with lytic phage on bacterial virulence-related traits are largely unknown. In this study we investigate the incidence of the mucoid phenotype of the bacterium Pseudomonas fluorescens SBW25 in response to co-evolution with the lytic phage phi2 (φ2). The mucoid phenotype of Pseudomonas spp. is due to overproduction of alginate and is a considerable virulence factor contributing to the intractability of infections most notably in cystic fibrosis (CF) lung, but also in pathogenic infections of plants. Our data show that this phenotype can evolve as an adaptive response to phage predation and is favoured under specific abiotic conditions, in particular a homogenous spatial structure and a high rate of nutrient replacement. The mucoid phenotype remains partially sensitive to phage infection, which facilitates ‘apparent competition'' with phage-sensitive competitors, partially offsetting the costs of alginate production. Although P. fluorescens SBW25 is not a pathogen, several key characteristics typical of Pseudomonas aeruginosa clinical isolates from CF lung were noted, including loss of motility on mucoid conversion and a high rate of spontaneous reversion to the wild-type phenotype. Although the genetic mechanisms of this phenotype remain unknown, they do not include mutations at many of the commonly reported loci implicated in mucoid conversion, including mucA and algU. These data not only further our understanding of the potential role phage have in the ecology and evolution of bacteria virulence in both natural and clinical settings, but also highlight the need to consider both biotic and abiotic variables if bacteriophages are to be used therapeutically. 相似文献
98.
The floral morphology of seven Oxypetalum species and, in particular, the spatial relationship between the five stigmatic chambers and two separate ovaries of their
flowers with respect to transmission of the pollen tube are studied. In all species, except O. banksii subsp. banksii, floral morphology is similar to that in other Asclepiadeae, and the flowers pollinated with one pollinium develop only one
follicle, which means compitum absence. In O. banksii subsp. banksii flowers, the secretory interstaminal tissue lines the inner walls of the stigmatic chambers as in the other species studied,
but it also reaches the upper part of the inner surface of the filament tube, where it surrounds the styles, an unprecedented
feature for Asclepiadaceae. This tissue secretes nectar and mucilage; the latter acts as transmitting medium for the growth
of pollen tubes from pollinia inserted and hydrated in stigmatic chambers (“hyperstigmas”). Mucilage also functions as an
extragynoecial compitum: in flowers pollinated with one pollinium both carpels develop into a follicle.
Received August 28, 2001; accepted April 9, 2002 Published online: October 14, 2002
Addresses of the authors: Milene Faria Vieira (e-mail: mfvieira@mail.ufv.br), Departamento de Biologia Vegetal, Universidade
Federal de Vi?osa, 36571-000, Vi?osa, Minas Gerais, Brazil. George John Shepherd, Departamento de Botanica, Instituto de Biologia,
Universidade Estadual de Campinas, C.P. 6109, 13083-970, Campinas, S?o Paulo, Brazil. 相似文献
99.
Kiyohiko Sugano 《化学与生物多样性》2009,6(11):2014-2029
Bile micelles play an important role in oral absorption of low‐solubility compounds. Bile micelles can affect solubility, dissolution rate, and permeability. For the pH–solubility profile in bile micelles, the Henderson–Hasselbalch equation should be modified to take bile‐micelle partition into account. For the dissolution rate, in the Nernst–Brunner equation, the effective diffusion coefficient in bile‐micelle media should be used instead of the monomer diffusion coefficient. The diffusion coefficient of bile micelles is 8‐ to 18‐fold smaller than that of monomer molecules. For permeability, the effective diffusion coefficient in the unstirred water layer adjacent to the epithelial membrane, and the free fraction at the epithelial membrane surface should be taken into account. The importance of these aspects is demonstrated here using several in vivo and clinical oral‐absorption data of low‐solubility model compounds. Using the theoretical equations, the food effect on oral absorption is further discussed. 相似文献
100.
V. Selvakumar P. R. Anbudurai T. Balakumar 《In vitro cellular & developmental biology. Plant》2001,37(2):280-284
Summary A protocol for rapid in vitro propagation using nodal explants obtained from 2-yr-old, field-grown medicinal plants of Plumbago zeylanica L. belonging to the family Plumbaginaceae is described. High frequency bud break and fast development of shoots were induced
on Murashige and Skoog's basal medium supplemented with 27.2 μM adenine sulfate +2.46 μM indole-3-butyric acid (IBA). Induction of rooting was achieved by transferring the shoots to the same basal medium containing
4.92 μM IBA. Using our protocol from one twig of P. zeylanica (eight responsive nodes per explant shoot) within a period of 5 mo., eight plantlets could be raised. After a hardening period
of 4 wk, there was a 90% transplantation success in the field compared to the 60–65% survival of plantlets recorded in the
experiments of previous workers. The plantlets derived through in vitro propagation mimic the growth and morphological characteristics of the donor plants. 相似文献