全文获取类型
收费全文 | 488974篇 |
免费 | 51974篇 |
国内免费 | 170篇 |
专业分类
541118篇 |
出版年
2018年 | 5878篇 |
2017年 | 5538篇 |
2016年 | 7685篇 |
2015年 | 10052篇 |
2014年 | 11422篇 |
2013年 | 15596篇 |
2012年 | 17871篇 |
2011年 | 17872篇 |
2010年 | 12057篇 |
2009年 | 10844篇 |
2008年 | 15581篇 |
2007年 | 15851篇 |
2006年 | 14957篇 |
2005年 | 13964篇 |
2004年 | 13890篇 |
2003年 | 12955篇 |
2002年 | 12560篇 |
2001年 | 18651篇 |
2000年 | 18680篇 |
1999年 | 14877篇 |
1998年 | 5554篇 |
1997年 | 5659篇 |
1996年 | 5287篇 |
1995年 | 4980篇 |
1994年 | 4766篇 |
1993年 | 4806篇 |
1992年 | 12099篇 |
1991年 | 11975篇 |
1990年 | 11677篇 |
1989年 | 11277篇 |
1988年 | 10844篇 |
1987年 | 10418篇 |
1986年 | 9673篇 |
1985年 | 9551篇 |
1984年 | 8075篇 |
1983年 | 6923篇 |
1982年 | 5377篇 |
1981年 | 4781篇 |
1980年 | 4622篇 |
1979年 | 7617篇 |
1978年 | 6065篇 |
1977年 | 5542篇 |
1976年 | 5311篇 |
1975年 | 5772篇 |
1974年 | 6491篇 |
1973年 | 6366篇 |
1972年 | 5933篇 |
1971年 | 5378篇 |
1970年 | 4797篇 |
1969年 | 4736篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
781.
Identification of actin-binding protein as the protein linking the membrane skeleton to glycoproteins on platelet plasma membranes 总被引:25,自引:0,他引:25
J E Fox 《The Journal of biological chemistry》1985,260(22):11970-11977
Platelets have previously been shown to contain a membrane skeleton that is composed of actin filaments, actin-binding protein, and three membrane glycoproteins (GP), GP Ib, GP Ia, and a minor glycoprotein of Mr = 250,000. The present study was designed to determine how the membrane glycoproteins were linked to actin filaments. Unstimulated platelets were lysed with Triton X-100, and the membrane skeleton was isolated on sucrose density gradients or by high-speed centrifugation. The association of the membrane glycoproteins with the actin filaments was disrupted when actin-binding protein was hydrolyzed by activity of the Ca2+-dependent protease, which was active in platelet lysates upon addition of Ca2+ in the absence of leupeptin. Similarly, activation of the Ca2+-dependent protease in intact platelets by the addition of a platelet agonist also caused the membrane glycoproteins to dissociate from the membrane skeleton. Affinity-purified actin-binding protein antibodies immunoprecipitated the membrane glycoproteins from platelet lysates in which actin filaments had been removed by DNase I-induced depolymerization and high-speed centrifugation. These results demonstrate that actin-binding protein links actin filaments of the platelet membrane skeleton to three plasma membrane glycoproteins and that filaments are released from their attachment site when actin-binding protein is hydrolyzed by the Ca2+-dependent protease within intact platelets during platelet activation. 相似文献
782.
N E Miller 《Biofeedback and self-regulation》1985,10(1):3-24
This paper will deal with a variety of topics such as dangers and opportunities from the developing crisis in health care costs, a cooperative study of the cost-effectiveness of treatments for headaches, the need for a federation of related societies, exploiting remarkable electronic advances, the wide range of adaptive functions of visceral learning (including its role in homeostasis), why maladjustments occur and their implications for biofeedback, and the need for analytic experiments involving adequate amounts of training. 相似文献
783.
Can a pore or pore-equivalent model account for transport of macromolecules across microvascular endothelium, or are alternate nonpore pathways necessary? Pores may be defined as aqueous channels of any shape or configuration, including those through a fiber matrix. Such pathways exhibit selective restriction to passage of macromolecules depending on their size, shape, and electrical charge. At least two pore pathways (small and large), differing in both sieve-element spacing and in hydraulic conductivity by an order of magnitude, are required to account for observed size selectivity for plasma proteins of similar shapes and charges. For the two organs examined critically in this review (cat ileum and dog paw), transport of macromolecules through small and large pore pathways is predominately convective. Total transport through small and large pores (alternatively, narrow and wide slits or fine and coarse fiber matrices) is insufficient to account for observed transport rates at low-to-moderate levels of volume flow. Either the estimated pore sizes and hydraulic conductivities derived from measurements of high volume-flow sieving are incorrect or other nonconvective transport pathways contribute substantially to macromolecular transport at low (normal) volume flow. 相似文献
784.
Species abundance distributions: pattern or process? 总被引:3,自引:1,他引:2
A. E. MAGURRAN 《Functional ecology》2005,19(1):177-181
785.
M. von Balthazar K. Raunsgaard Pedersen E. M. Friis 《Plant Systematics and Evolution》2005,255(1-2):55-75
A charcoalified fossil flower bud of a new genus and species (Teixeiria lusitanica) is described from the Early Cretaceous of Portugal. The flower is actinomorphic and unisexually male. At the base of the
bud there are several bracts of different sizes, which are followed by sepal-like and petal-like tepals. Bracts and perianth
organs seem to be arranged spirally and to exhibit transitions between different organ categories. The androecium has numerous
stamens in two sizes, but with unclear arrangement. Pollen is small and tricolpate with a perforate tectum and a densely columellate
infratectal layer. No carpels or remains of carpels could be observed on the floral axis. Teixeiria lusitanica shows most affinities to members of Ranunculales. There are also some similarities with Berberidopsis (Berberidopsidaceae, Berberidopsidales) and members of the Saxifragales (Hamamelidaceae and Daphniphyllaceae). 相似文献
786.
787.
R.E. Jonkers B. Oosterhuis R.J.M. Ten Berge C.J. Van Boxtel 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1982,233(1):249-255
A relatively simple assay with improved reliability and sensitivity for measuring levels of 6-mercaptopurine in human plasma is presented. After extraction of the compound and the added internal standard with phenyl mercury acetate, samples were separated by ion-pair reversed-phase high-performance liquid chromatography. On-line the analytes were oxidized to fluorescent products and detected in a flow-fluorimeter. The within-day coefficient of variation was 3.8% at a concentration of 25 ng/ml. The lower detection limit was 2 ng/ml when 1.0 ml of plasma was used. Mercaptopurine concentration versus time curves of two subjects after a single oral dose of azathioprine are shown. 相似文献
788.
The DNA of fifteen Italian cultivars of durum wheat (Triticum turgidum L. ssp. durum) were analyzed by in fluorescence amplified fragment length polymorphism (fAFLP) in order to obtain the characteristic fingerprintings
of genotypes and assess their genetic relatedness. Among 64 combinations of fluorescence labelled primers, three different
combinations were chosen as producing a total of 6630 AFLP fragments, 2277 (34.3 %) of them being polymorphic. By using this
fAFLP methodology a DNA fingerprinting of each durum wheat cultivar was generated for genotype identification. Analysis of
the genetic relationships show the low variability among durum wheat cultivars. 相似文献
789.
S L Rakestraw W E Ford R G Tompkins M A Rodgers W P Thorpe M L Yarmush 《Biotechnology progress》1992,8(1):30-39
A set of anti-melanoma immunoconjugates were prepared which contained chlorin e6: antibody molar ratios of 18.9:1, 11.2:1, 6.8:1, and 1.7:1. All immunoconjugates retained antigen binding activity regardless of the chromophore:antibody substitution ratio that was attained. In contrast, the ground-state absorption spectra of the immunoconjugates showed features which appeared to be dependent on the chromophore:antibody molar ratio. In addition, the quantum yield of singlet oxygen generated by the conjugated chromophores was observed to be significantly less than that observed with the unbound dye. Time-resolved absorbance spectroscopy of the chromophore excited triplet state indicated that the loss of singlet oxygen quantum yield resulted from diminished chromophore triplet yield. Analysis of data obtained from in vitro photolysis of target melanoma cells, in combination with that obtained from the immunochemical and photochemical studies, indicates that the observed immunoconjugate phototoxicity can be reasonably quantitatively represented by (1) the ability of the immunoconjugate to bind SK-MEL-2 cell surface antigen, (2) the amount of chromophore localized at the target cells by immunoconjugate binding, (3) the delivered dose of light at 634 nm, and (4) the singlet oxygen quantum yield of the antibody-bound photosensitizer. Though these data argue strongly for photolysis by the cumulative dosage of singlet oxygen at the cell membrane, nonetheless, the concurrent photoinduced release of other cytotoxic agents should not be ruled out. 相似文献
790.