全文获取类型
收费全文 | 127143篇 |
免费 | 10897篇 |
国内免费 | 7120篇 |
专业分类
145160篇 |
出版年
2024年 | 220篇 |
2023年 | 1486篇 |
2022年 | 3319篇 |
2021年 | 5633篇 |
2020年 | 3699篇 |
2019年 | 4533篇 |
2018年 | 4585篇 |
2017年 | 3432篇 |
2016年 | 4925篇 |
2015年 | 7044篇 |
2014年 | 8331篇 |
2013年 | 8880篇 |
2012年 | 10558篇 |
2011年 | 9589篇 |
2010年 | 5895篇 |
2009年 | 5202篇 |
2008年 | 6147篇 |
2007年 | 5463篇 |
2006年 | 4913篇 |
2005年 | 3832篇 |
2004年 | 3388篇 |
2003年 | 2989篇 |
2002年 | 2645篇 |
2001年 | 3949篇 |
2000年 | 3688篇 |
1999年 | 3111篇 |
1998年 | 1422篇 |
1997年 | 1569篇 |
1996年 | 1381篇 |
1995年 | 1270篇 |
1994年 | 1207篇 |
1993年 | 886篇 |
1992年 | 1647篇 |
1991年 | 1386篇 |
1990年 | 1083篇 |
1989年 | 925篇 |
1988年 | 763篇 |
1987年 | 644篇 |
1986年 | 548篇 |
1985年 | 509篇 |
1984年 | 295篇 |
1983年 | 267篇 |
1982年 | 184篇 |
1981年 | 159篇 |
1980年 | 142篇 |
1979年 | 148篇 |
1978年 | 107篇 |
1976年 | 88篇 |
1974年 | 99篇 |
1973年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
E A Rinnooy Kan E Platzer K Welte C Y Wang 《Journal of immunology (Baltimore, Md. : 1950)》1984,133(6):2979-2985
We investigated the influence of monocytes on the susceptibility of the T3 antigen on human T cells to modulation induction by OKT3 antibody. In the absence of monocytes, the T3 antigen was only minimally susceptible to modulation. After the addition of 20% monocytes to the culture, however, complete modulation was readily observed. Furthermore, we found that even in the absence of OKT3 antibody, monocytes were able to down-regulate the expression of the T3 antigen, although to a lesser extent. The ability of monocytes to enhance antigenic modulation proved to be a more general phenomenon. Each individual T cell antigen, however, differed in its susceptibility to modulation by antibody, monocytes, or both, thereby establishing its own characteristic pattern. In addition, after complete modulation of the T3 antigen, the addition of monocytes to the culture thereafter had a distinct inhibitory effect on the reexpression of the T3 antigen. Monocyte enhancement of T3 modulation is significantly reduced when using the OKT3 F(ab')2 fragment, as is OKT3 mitogenesis. After pulsing the monocytes with OKT3 antibody before adding them to the culture, T3 modulation became nearly complete even in the absence of added OKT3 antibody. Monocyte-induced modulation proved not to be MHC restricted, thus allowing for comparative analysis of this effect between monocytes and other cell types. A moderate, however, incomplete modulation enhancement was observed with the human monocyte cell line U937 and with Daudi cells. This finding proved to coincide with the distinct ability of these cell lines to bind OKT3 antibody by their Fc receptors, as was the case with monocytes. In contrast, neither Fc receptor binding nor T3 modulation enhancement was observed with the cell lines Cess and G7. In addition, no effective T3 modulation was observed with glutaraldehyde-fixed monocytes. The overall results seem to indicate that effective modulation of the T3 antigen by OKT3 antibody requires the active participation of Fc receptors on monocytes. 相似文献
93.
Summary The immunohistochemical localization of neuropeptide Y (NPY) was correlated with those of dopamine--hydroxylase (DBH) and vasoactive intestinal polypeptide (VIP) by mapping serial 7 m paraffin sections at three levels of the guina pig lower brainstem: a) area postrema, b) dorsal motor nucleus of the vagus, and c) nucleus prepositus of the hypoglossal nerve. Based on differences in transmitter expression, three populations of NPY-immunoreactive (IR) neurons were distinguished: NPY-IR catecholaminergic cells (NPY/CA), NPY-IR VIP-ergic cells (NPY/VIP), and NPY-IR cells which were not reactive to either DBH or VIP. Within these populations, size differences among neurons in characteristic locations allowed differentiation among the following subpopulations: NPY/CA neurons in the lateral reticular nucleus — magnocellular part (mean neuronal size 538 m2) and parvocellular part (318 m2)-, in the vagus-solitarius complex (433 m2), and in the dorsal strip (348 m2); NPY/VIP neurons in the vagus-solitarius complex (368 m2) and in the nucleus ovalis (236 m2). Apart from scattered NPY-IR cell bodies in the regions listed above, NPY-IR cell bodies in the lateral portion of the nucleus solitarius and in the caudal part of the spinal nucleus of the trigeminal nerve did not exhibit IR to either DBH or VIP. NPY-IR neurons in the area postrema occurred too infrequently for co-localization studies. The differential distribution of heterogeneous NPY-IR cell subpopulations may reflect the involvement of NPY in a variety of neuronal functions.Supported by the Deutsche Forschungsgemeinschaft, grant He 919/6-1 相似文献
94.
Application of macroscopic balances to the identification of gross measurement errors 总被引:1,自引:0,他引:1
A systematic method is presented which is capable of both detecting the presence of grossly biased measurement errors and locating the source of these errors in a bioreactor through statistical hypothesis testing. Equality constraints derived from material and energy balances are employed for the detection of data inconsistencies and for the subsequent identification of the suspect measurements by a process of data analysis and rectification. Maximum likelihood techniques are applied to the estimation of the states and parameters of the bioreactor after the suspect measurements have been eliminated. The level of significance is specified by the experimenter while the measurments are assumed to be randomly, normally distributed with zero mean and known variances. Two different approaches of data analysis, batchwise and sequential, that lead to a consistent set of adjustments on the experimental values, are discussed. Several examples based on the fermentation data taken from literature sources are presented to demonstrate the utility of the proposed method, and one set of data is solved numerically to illustrate the computational aspect of the algorithm. 相似文献
95.
The UDS induced in cultured FL cells by exposure to chemicals was measured as hydroxyurea-resistant incorporation of 3H-TdR in the acid-insoluble fraction of the 14C-TdR-prelabelled cells synchronized by the combination of arginine starvation and pretreatment with hydroxyurea. The level of UDS is represented by the ratios of 3H/14C radioactivities which are measures of specific activities of 3H. Two direct-acting alkylating agents, MMS and MNNG, a cross-linking agent, mitomycin C, and 3 procarcinogens, B(a)P, AFB1 and cyclophosphamide elicited UDS in the absence or presence of the liver-metabolizing system. Three chemicals of unknown carcinogenicity were also able to induce UDS in this assay system, i.e., bis-(O,O-diethylphosphinothioyl)-disulphide, 4-chlorophenoxy acetic acid (sodium salt) and caramelized malt sugar. With the exception of 4-chlorophenoxy acetic acid, they were also active in the Ames test. 相似文献
96.
97.
Some properties of phospholipases of alveolar macrophages 总被引:6,自引:0,他引:6
98.
99.
100.