全文获取类型
收费全文 | 3255篇 |
免费 | 214篇 |
出版年
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 53篇 |
2020年 | 39篇 |
2019年 | 58篇 |
2018年 | 81篇 |
2017年 | 57篇 |
2016年 | 83篇 |
2015年 | 136篇 |
2014年 | 145篇 |
2013年 | 228篇 |
2012年 | 246篇 |
2011年 | 257篇 |
2010年 | 154篇 |
2009年 | 124篇 |
2008年 | 218篇 |
2007年 | 220篇 |
2006年 | 184篇 |
2005年 | 152篇 |
2004年 | 150篇 |
2003年 | 162篇 |
2002年 | 159篇 |
2001年 | 27篇 |
2000年 | 16篇 |
1999年 | 26篇 |
1998年 | 27篇 |
1997年 | 33篇 |
1996年 | 20篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 22篇 |
1992年 | 28篇 |
1991年 | 27篇 |
1990年 | 27篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1971年 | 4篇 |
排序方式: 共有3469条查询结果,搜索用时 31 毫秒
1.
E Imbasciati R Gusmano A Edefonti P Zucchelli C Pozzi C Grassi M Della Volpe F Perfumo P Petrone M Picca et al. 《BMJ (Clinical research ed.)》1985,291(6505):1305-1308
In a multicentre, randomised, prospective trial 89 patients (67 children and 22 adults) with the minimal change nephrotic syndrome were treated with three intravenous pulses of methylprednisolone followed by low dose oral prednisone for six months (group given methylprednisolone) or with high dose oral prednisone for four weeks followed by low dose oral prednisone for five months (control group). Five patients in the group given methylprednisolone and one in the control group did not respond initially. The time to response was shorter in children treated with methylprednisolone. No significant differences between the two groups were observed in the number of patients who relapsed or number of relapses per patient per year. Patients given methylprednisolone tended to relapse earlier than patients in the control group. Side effects related to treatment were significantly fewer in the group given methylprednisolone than in the control group. These data suggest that a short course of methylprednisolone pulses followed by low dose oral prednisone is only marginally less effective than a regimen of high dose oral steroids but can improve the ratio of risk to benefit associated with treatment of the minimal change nephrotic syndrome. 相似文献
2.
3.
4.
5.
Internal Representations of Temporal Statistics and Feedback Calibrate Motor-Sensory Interval Timing
Humans have been shown to adapt to the temporal statistics of timing tasks so as to optimize the accuracy of their responses, in agreement with the predictions of Bayesian integration. This suggests that they build an internal representation of both the experimentally imposed distribution of time intervals (the prior) and of the error (the loss function). The responses of a Bayesian ideal observer depend crucially on these internal representations, which have only been previously studied for simple distributions. To study the nature of these representations we asked subjects to reproduce time intervals drawn from underlying temporal distributions of varying complexity, from uniform to highly skewed or bimodal while also varying the error mapping that determined the performance feedback. Interval reproduction times were affected by both the distribution and feedback, in good agreement with a performance-optimizing Bayesian observer and actor model. Bayesian model comparison highlighted that subjects were integrating the provided feedback and represented the experimental distribution with a smoothed approximation. A nonparametric reconstruction of the subjective priors from the data shows that they are generally in agreement with the true distributions up to third-order moments, but with systematically heavier tails. In particular, higher-order statistical features (kurtosis, multimodality) seem much harder to acquire. Our findings suggest that humans have only minor constraints on learning lower-order statistical properties of unimodal (including peaked and skewed) distributions of time intervals under the guidance of corrective feedback, and that their behavior is well explained by Bayesian decision theory. 相似文献
6.
Sequence complexity and diversity of polyadenylated RNA molecules transcribed in human myeloid cells
7.
8.
Alberto Buson Alessandro Negro Luigi Grassato Massimo Tagliaro Marina Basaglia Claudio Grandi Angelo Fontana Marco P. Nuti 《FEMS microbiology letters》1996,145(1):55-62
Abstract A clone positive for d-carbamoylase activity (2.7 kb Hin dIII- Bam H1 DNA fragment) was obtained by screening a genomic library of Agrobacterium radiobacter in Escherichia coli . This DNA fragment contains an open reading frame of 912 bp which is predicted to encode a peptide of 304 amino acids with a calculated molecular mass of 34247 Da. The d-carbamoylase gene. named cauA , was placed under the control of T7 RNA-dependent promoter and expressed in E. coli BL21 (DE3). After induction with isopropyl-thio-β-d-galactopyranoside, the synthesis of d-carbamoylase in E. coli reached about 40% of the total protein. The expressed protein was shown to possess a molecular mass, on SDS-PAGE, of 36 kDa and showed an enhanced allowed us to establish that a Pro14 →Leu14 exchange leads to an inactive enzyme species, while a Cys279 →Ser279 exchange did not impair the functional properties of the enxyme. 相似文献
9.
Summary Binding of azide to a series of copper(II) complexes has been investigated by absorption, CD and EPR spectroscopy. Axial binding of azide to Cu(II) can be differentiated from equatorial binding through the lower intensity and lack of optical activity of the LMCT band. The affinity of azide for Cu(II) increases with the overall positive charge of the complex. The preliminary data on thiocyanate binding to Cu(II) seem to agree with the trends observed for the corresponding azide adducts. 相似文献
10.
Alessandra Faraoni Roberto Santucci Luigi Campanella Gloria Tranchida Maurizio Brunori 《Biometals》1990,3(2):122-124
Summary The electrochemical behaviour of Fe(III)-protoporphyrin IX entrapped into a cellulose triacetate membrane has been investigated by cyclic voltammetry. The physical entrapment into a solid matrix does not modify the redox properties of the entrapped berries, which also act as efficient promoters in the electrochemistry of cytochromec. Such a system represents a promising example of a simple solid-state promoter, and stimulates further investigations in order to obtain more complex systems that may be of significance for basic and applied bioelectrochemistry. 相似文献