全文获取类型
收费全文 | 47930篇 |
免费 | 4291篇 |
国内免费 | 744篇 |
出版年
2021年 | 836篇 |
2020年 | 584篇 |
2019年 | 804篇 |
2018年 | 939篇 |
2017年 | 722篇 |
2016年 | 1170篇 |
2015年 | 1888篇 |
2014年 | 2059篇 |
2013年 | 2704篇 |
2012年 | 3031篇 |
2011年 | 2896篇 |
2010年 | 2018篇 |
2009年 | 1585篇 |
2008年 | 2280篇 |
2007年 | 2144篇 |
2006年 | 2053篇 |
2005年 | 1852篇 |
2004年 | 1826篇 |
2003年 | 1725篇 |
2002年 | 1717篇 |
2001年 | 1508篇 |
2000年 | 1356篇 |
1999年 | 1228篇 |
1998年 | 585篇 |
1997年 | 580篇 |
1996年 | 444篇 |
1995年 | 464篇 |
1994年 | 375篇 |
1993年 | 394篇 |
1992年 | 776篇 |
1991年 | 749篇 |
1990年 | 668篇 |
1989年 | 643篇 |
1988年 | 533篇 |
1987年 | 489篇 |
1986年 | 467篇 |
1985年 | 535篇 |
1984年 | 468篇 |
1983年 | 402篇 |
1982年 | 310篇 |
1981年 | 325篇 |
1980年 | 261篇 |
1979年 | 380篇 |
1978年 | 329篇 |
1977年 | 333篇 |
1976年 | 317篇 |
1975年 | 335篇 |
1974年 | 331篇 |
1973年 | 313篇 |
1972年 | 248篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
André De Troyer 《Journal of applied physiology》2005,98(3):795-803
Changes in intrathoracic pressure produced by the various inspiratory intercostals are essentially additive, but the interaction between these muscles and the diaphragm remains uncertain. In the present study, this interaction was assessed by measuring the changes in airway opening (DeltaPao) or transpulmonary pressure (DeltaPtp) in vagotomized, phrenicotomized dogs during spontaneous inspiration (isolated intercostal contraction), during isolated rectangular or ramp stimulation of the peripheral ends of the transected C(5) phrenic nerve roots (isolated diaphragm contraction), and during spontaneous inspiration with superimposed phrenic nerve stimulation (combined diaphragm-intercostal contraction). With the endotracheal tube occluded at functional residual capacity, DeltaPao during combined diaphragm-intercostal contraction was nearly equal to the sum of the DeltaPao produced by the two muscle groups contracting individually. However, when the endotracheal tube was kept open, DeltaPtp during combined contraction was 123% of the sum of the individual DeltaPtp (P < 0.001). The increase in lung volume during combined contraction was also 109% of the sum of the individual volume increases (P < 0.02). Abdominal pressure during combined contraction was invariably lower than during isolated diaphragm contraction. It is concluded, therefore, that the canine diaphragm and intercostal muscles act synergistically during lung expansion and that this synergism is primarily due to the fact that the intercostal muscles reduce shortening of the diaphragm. When the lung is maintained at functional residual capacity, however, the synergism is obscured because the greater stiffness of the rib cage during diaphragm contraction enhances the DeltaPao produced by the isolated diaphragm and reduces the DeltaPao produced by the intercostal muscles. 相似文献
52.
Lusinete Aciole De Queiroz 《Mycopathologia》1973,51(4):307-314
A new species of the genusEndomycopsis is proposed. It was isolated from waste water, at Montevideo-Uruguay.By its morphological and biochemical proprieties it differs from allEndomycopsis previously described.
Este trabajo fue desarrollado en el Laboratorio de Micologia de la Facultad de Química de Montevideo, Uruguay y en uso de una beca de la Universidad Federal de Pernambuco para perfecciobamiento en el estudio de las levaduras. 相似文献
Este trabajo fue desarrollado en el Laboratorio de Micologia de la Facultad de Química de Montevideo, Uruguay y en uso de una beca de la Universidad Federal de Pernambuco para perfecciobamiento en el estudio de las levaduras. 相似文献
53.
Isolation of Temperature-Sensitive Membrane Mutants of Escherichia coli K-12 总被引:1,自引:1,他引:0 下载免费PDF全文
Johan F. Steenbakkers J. H. F. F. Broekman A. Kerkenaar P. G. De Haan 《Journal of bacteriology》1973,116(2):535-540
Mutants with impaired biosynthesis of unsaturated fatty acids or altered metabolism of the phospholipids were isolated at a rather high frequency from a set of temperature-sensitive lysis mutants. It is suggested that preselection for the lysis phenotype makes it possible to isolate several kinds of mutants affected in the integrity of the cytoplasmic membrane. 相似文献
54.
Physiological and Biochemical Mechanisms Involved in the Response to Abscisic Acid in Maize Coleoptiles 总被引:2,自引:0,他引:2
The role of abscisic acid (ABA) in controlling growth and developmenthas been studied in maize (Zea mays L.) coleoptile segments.Application of ABA reduces the elongation rate by about 50%and affects ion fluxes. In particular, proton extrusion is decreasedwhile potassium efflux is greatly enhanced. Apparently, ABAdoes not: seem to influence calcium influx from the apoplastinto the cytosol, but more likely it influences its efflux.Alteration of cytosolic calcium concentration may also be obtainedby increasing its release from internal stores. This possibilitymight be sustained by the increased hydrolysis of phosphatidylinositolupon ABA application. Change in the balance of ion fluxes shouldresult from regulation of transport mechanisms at the membranelevel and should produce changes in the transmembrane electricalpotential. The H+- ATPase and the ATP-dependent calcium transportactivities are both influenced by the treatment with ABA, 55%and 40%, respectively. Under these conditions [Ca2+]cytand pHcyt can be modified and, as a consequence of their regulation,they may play an important role in mediating the physiologicaland biochemical effects of ABA, acting as second intracellularmessengers.
1Research supported by National Research Council of Italy, SpecialProject RAISA, Sub-Project N. 2, Paper n. 2782. 相似文献
55.
C. S. Lin M. C. Tseng P. I. Hong W. C. Chang 《In vitro cellular & developmental biology. Plant》2006,42(4):331-335
Summary Inflorescence proliferation is a plant tissue culture technique that, can be used to obtain in vitro inflorescences year-round without the intervening development of vegetative organs. In this study, we used albino mutant
inflorescences of Dendrocalamus latiflorus as the original explant material to investigate, the effect of plant growth regulators on long-term inflorescence proliferation.
The albino inflorescences proliferated on solidified Murashige and Skoog (MS) basal medium supplemented with thidiazuron (TDZ),
and the optimal concentration for successful long-term inflorescence proliferation was 0.45 μM TDZ. A combination of α-naphthaleneacetic acid (NAA) with 0.45 μM TDZ inhibited the inflorescence proliferation. Inflorescences cultured on a TDZ-free medium supplemented with 26.82 μM NAA rooted in 21 d, vegetative shoots formed by 42 d and, in one case, flowering occurred after 63 d. The auxins 2,4-dichlorophenoxyacetic
acid (2,4-D, 4.52 μM) and pieloram (4.14 μM) induced shoot formation. The protocol described can be used to produce large numbers of mutant inflorescences within a relatively
short period of time. 相似文献
56.
I De Carneri 《Parassitologia》1971,13(1):165-167
57.
野大豆叶绿体在低温(77K)时出现三条荧光发射谱带,它们来源于不同的色素蛋白复合体。 在纳秒脉冲激光激发下,捕光天线色素的相对荧光量子产额,随激光强度的增加有明显下降现象。用激子理论和动力学方程讨论和计算了激子扩散参量。指出激子转移是随机的,非相干的。 相似文献
58.
59.
Chien-Hung Liu Wen-Ming Chen Jo-Shu Chang 《World journal of microbiology & biotechnology》2007,23(5):633-640
Acidic lipase finds its commercial values in medical applications and bioremediation of food wastes. In this work, approaches
for rapid screening of lipase-producing bacteria were developed and the feasibility assessment of the screening methods was
performed. From food waste samples, the proposed screening procedures allowed isolation of sixteen pure bacterial strains
expressing higher lipase activity at acidic pH (pH 6.0) than at alkaline pH (pH 9.0). To enhance the accuracy of lipase activity
determination under acidic conditions, a novel assay procedure was also developed by deactivating lipase activity by microwave
treatment prior to back titration. This additional step could minimize interferences arising from residual lipase activity
during conventional direct back-titration methods in measuring lipase activity at acidic pH. Using the four strategies proposed
in this work, the best acidic-lipase-producing isolate was obtained by strategy C (SSC) and was identified as Aeromonas sp. C14, displaying an optimal lipase activity of 0.7 U/ml at an acidic pH of 6.0. 相似文献