全文获取类型
收费全文 | 22813篇 |
免费 | 2279篇 |
国内免费 | 15篇 |
出版年
2023年 | 90篇 |
2022年 | 194篇 |
2021年 | 383篇 |
2020年 | 263篇 |
2019年 | 298篇 |
2018年 | 345篇 |
2017年 | 378篇 |
2016年 | 522篇 |
2015年 | 909篇 |
2014年 | 1027篇 |
2013年 | 1135篇 |
2012年 | 1605篇 |
2011年 | 1603篇 |
2010年 | 1062篇 |
2009年 | 948篇 |
2008年 | 1299篇 |
2007年 | 1439篇 |
2006年 | 1139篇 |
2005年 | 1200篇 |
2004年 | 1183篇 |
2003年 | 1124篇 |
2002年 | 1071篇 |
2001年 | 359篇 |
2000年 | 337篇 |
1999年 | 319篇 |
1998年 | 299篇 |
1997年 | 198篇 |
1996年 | 156篇 |
1995年 | 149篇 |
1994年 | 167篇 |
1993年 | 161篇 |
1992年 | 211篇 |
1991年 | 223篇 |
1990年 | 177篇 |
1989年 | 178篇 |
1988年 | 178篇 |
1987年 | 173篇 |
1986年 | 163篇 |
1985年 | 187篇 |
1984年 | 183篇 |
1983年 | 138篇 |
1982年 | 112篇 |
1981年 | 138篇 |
1980年 | 112篇 |
1979年 | 110篇 |
1978年 | 109篇 |
1977年 | 88篇 |
1976年 | 97篇 |
1974年 | 106篇 |
1973年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In social environments, decisions not only determine rewards for oneself but also for others. However, individual differences in pro-social behaviors have been typically studied through self-report. We developed a decision-making paradigm in which participants chose from card decks with differing rewards for themselves and charity; some decks gave similar rewards to both, while others gave higher rewards for one or the other. We used a reinforcement-learning model that estimated each participant''s relative weighting of self versus charity reward. As shown both in choices and model parameters, individuals who showed relatively better learning of rewards for charity – compared to themselves – were more likely to engage in pro-social behavior outside of a laboratory setting indicated by self-report. Overall rates of reward learning, however, did not predict individual differences in pro-social tendencies. These results support the idea that biases toward learning about social rewards are associated with one''s altruistic tendencies. 相似文献
52.
Ethical Considerations for Outcome‐adaptive Trial Designs: A Clinical Researcher's Perspective
下载免费PDF全文
![点击此处可从《Bioethics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Scott Brian Saxman 《Bioethics》2015,29(2):59-65
In a typical comparative clinical trial the randomization scheme is fixed at the beginning of the study, and maintained throughout the course of the trial. A number of researchers have championed a randomized trial design referred to as ‘outcome‐adaptive randomization.’ In this type of trial, the likelihood of a patient being enrolled to a particular arm of the study increases or decreases as preliminary information becomes available suggesting that treatment may be superior or inferior. While the design merits of outcome‐adaptive trials have been debated, little attention has been paid to significant ethical concerns that arise in the conduct of such studies. These include loss of equipoise, lack of processes for adequate informed consent, and inequalities inherent in the research design which could lead to perceptions of injustice that may have negative implications for patients and the research enterprise. This article examines the ethical difficulties inherent in outcome‐adaptive trials. 相似文献
53.
To investigate changes in surface proteins of uterine cells in relation to the time of implantation, epithelial and stromal cells were isolated from rabbit endometrium and maintained in primary culture for 3 days. Surface-iodination of intact cells was carried out before and after culture, using immobilized Iodogen catalyst. The labeled proteins were analyzed by polyacrylamide gel electrophoresis, followed by autoradiography; peak areas were quantitated by scanning densitometry. Different gestational ages showed no marked qualitative differences in the surface-iodination patterns either of epithelial or stromal cells before or after culture. Quantitative differences between the surface-iodination pattern of epithelial cells from days 4 to 6.5 of pregnancy were revealed by canonical variate analysis of labeled peak areas. Values for individual rabbits clustered according to gestational age, with significant (p less than 0.05) separation of the clusters, although the discrimination was less pronounced for cultured than for freshly isolated cells. Changes involving increases in labeling of a protein of 38000 Mr in fresh cells, and decreases in a protein of 42000 Mr in cultured cells, were evident between day 4 and day 6.5. Thus changes in the surface-labeling pattern of uterine epithelial cells in relation to the time of receptivity for ovoimplantation can be distinguished. The functional significance of these changes remains to be elucidated. 相似文献
54.
Mitosis is the key event of the cell cycle during which the sister chromatids are segregated onto two daughter cells. It is well established that abrogation of the normal mitotic progression is a highly efficient concept for anti‐cancer treatment. In fact, various drugs that target microtubules and thus interfere with the function of the mitotic spindle are in clinical use for the treatment of various human malignancies for many years. However, since microtubule inhibitors not only target proliferating cells severe side effects limit their use. Therefore, the identification of novel mitotic drug targets other than microtubules have gained recently much attention. This review will summarize the latest developments on the identification and clinical evaluation of novel mitotic drug targets and will introduce novel concepts for chemotherapy that are based on recent progress in our understanding how mitotic progression is regulated and how anti‐mitotic drugs induce tumor cell death. J. Cell. Biochem. 111: 258–265, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
55.
Gerald Scott 《Free radical research》1988,5(3):141-147
Antioxidants and stabilisers are of critical importance in the manufacture and use of polymer artifacts. Most conventional additives are readily leached from plastics or rubbers by foodstuffs or body fluids with consequent danger associated with the potential toxicity in the body. Strategy for the development of biologically “safe” stabilisation systems for polymers are discussed and it is concluded that the attachment of the appropriate reactive functional group to the polymer backbone by “reactive processing” provides the best means of immobilising the functional group to leaching fluids without sacrificing its protective action. 相似文献
56.
Denise K. Garcia Scott K. Davis 《Evolution; international journal of organic evolution》1994,48(2):376-391
Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics. 相似文献
57.
58.
59.
Phillip Cribb 《Curtis's Botanical Magazine》2005,22(1):22-24
Summary. The golden‐flowered Masdevallia niesseniae Luer from Colombia is described and illustrated from the type collection. 相似文献
60.
Anton Pauw Sunshine A. Van Bael Halton A. Peters Steven D. Allison José L. C. Camargo Miguel Cifuentes-Jara Aurlstela Conserva Teresa Garcia Restom Tamara Heartsill-Scalley Scott A. Mangan Gabriela Nunez-lturri Elsie Rivera-Ocasio Mark Rountree Susanne Vetter Carolina Volkmer de Castllho 《Biotropica》2004,36(3):410-413