全文获取类型
收费全文 | 2585篇 |
免费 | 420篇 |
国内免费 | 492篇 |
出版年
2024年 | 15篇 |
2023年 | 69篇 |
2022年 | 56篇 |
2021年 | 98篇 |
2020年 | 142篇 |
2019年 | 169篇 |
2018年 | 147篇 |
2017年 | 154篇 |
2016年 | 161篇 |
2015年 | 146篇 |
2014年 | 162篇 |
2013年 | 184篇 |
2012年 | 142篇 |
2011年 | 135篇 |
2010年 | 121篇 |
2009年 | 137篇 |
2008年 | 143篇 |
2007年 | 147篇 |
2006年 | 167篇 |
2005年 | 129篇 |
2004年 | 112篇 |
2003年 | 121篇 |
2002年 | 94篇 |
2001年 | 72篇 |
2000年 | 81篇 |
1999年 | 63篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 20篇 |
1993年 | 22篇 |
1992年 | 13篇 |
1991年 | 19篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3497条查询结果,搜索用时 62 毫秒
91.
A variety of epidemiologic studies have focused on the association between macrophage migration inhibitory factor (MIF) gene − 173G/C polymorphism and inflammatory bowel disease (IBD). However, results in different studies have been inconsistent. In order to derive a more precise estimation of the associations, we performed this meta-analysis and systematic searches of electronic databases PubMed and Web of Science (up to April 30, 2013). Based on our search criteria, a total of seven eligible studies concerning the MIF − 173G/C polymorphism and IBD risk were included in the final meta-analysis, comprising 2162 IBD cases and 2134 controls. Significant association was found between MIF − 173G/C polymorphism and the risk of IBD when all studies were pooled into the meta-analysis (for C allele vs. G allele: OR = 1.25, 95% CI = 1.12–1.41, p = 0.000; for C/C vs. G/G: OR = 1.71, 95% CI = 1.23–2.39, p = 0.002; for C/C + G/C vs. G/G: OR = 1.24, 95% CI = 1.09–1.42, p = 0.002; for C/C vs. G/C + G/G: OR = 1.67, 95% CI = 1.20–2.33, p = 0.002). Heterogeneity and publication bias did not exist in the overall comparisons. The present meta-analysis suggests an association between the MIF − 173G/C polymorphism and IBD risk. However, due to few studies and the selection bias existed in some studies, the results should be interpreted with caution. 相似文献
92.
Bioinformatics tools have facilitated the reconstruction and analysis of cellular metabolism of various organisms based on information encoded in their genomes. Characterization of cellular metabolism is useful to understand the phenotypic capabilities of these organisms. It has been done quantitatively through the analysis of pathway operations. There are several in silico approaches for analyzing metabolic networks, including structural and stoichiometric analysis, metabolic flux analysis, metabolic control analysis, and several kinetic modeling based analyses. They can serve as a virtual laboratory to give insights into basic principles of cellular functions. This article summarizes the progress and advances in software and algorithm development for metabolic network analysis, along with their applications relevant to cellular physiology, and metabolic engineering with an emphasis on microbial strain optimization. Moreover, it provides a detailed comparative analysis of existing approaches under different categories. 相似文献
93.
T. Jebali W. Moalla M. Elloumi J. Padulo G. Baquet K. Chamari 《Biology of sport / Institute of Sport》2013,30(3):219-225
The aim of this study was to investigate the heart rate (HR) responses, the rate of perceived exertion (RPE), and the feeling during physical education schooling while performing traditional games activities compared to intermittent exercise. Nineteen pre-pubertal children randomly performed on different days two types of lessons (intermittent running mode vs. traditional Tunisian “Raqassa” game) lasting 12-min each. HR was continuously recorded during both lessons, while ratings of perceived exertion and Feeling values were recorded after the sessions. The mean HR value during the traditional game was significantly higher than during intermittent exercise (p<0.05). Conversely, the perceived exertion score was significantly higher after intermittent exercise than the traditional exercise game (p<0.05), showing that the higher cardiovascular strain of the game was perceived as “lighter” than the run. Simultaneously, the children''s Feeling was significantly higher after the traditional game than intermittent exercise (p<0.001), showing a higher satisfaction from playing with respect to running. Exercise based on the “Raqassa” traditional game could be used in pre-pubertal children as an alternative or as an additional method for suitable cardiovascular stimulation during physical education lessons with lower perceived exertion and better feeling compared to intermittent running. 相似文献
94.
Gladbachus adentatus is a putative chondrichthyan, known only from the holotype specimen, which comprises an articulated endoskeleton complete from head to pelvic region with the squamation also preserved. The scales superficially resemble those of placoderms more than sharks, in having a similar gross morphology, lamellar cellular bone forming the base and upright dentinous tubercles comprising the crown. The odontocytic mesodentine in the tubercles is comparable to that in the Osteostraci and in some acanthodian taxa, known only from isolated scales, and is probably the plesiomorphic form of dentine for Gnathostomata. 相似文献
95.
《Anthrozo?s》2013,26(4):332-342
AbstractStudies have explored the motivations behind the decision to become vegetarian, and have explored the well being of vegetarians. However, little research has focused on the social psychological and interpersonal aspects of vegetarianism. The focus of this study was to develop a scale designed to measure attitudes toward vegetarians (ATVS). This scale measures a one-factor construct with adequate internal consistency. The ATVS correlated significantly with the construct of authoritarianism, and, as expected, the ATVS did not correlate significantly with social desirability. In addition, attitudes toward vegetarians were found to be generally positive. The positive attitudes toward vegetarians may be the result of using a college student population that was overwhelmingly female. 相似文献
96.
Rong Huang Daifang Wang Shuzhen Liu Longhua Guo Fangfang Wang Zhenyu Lin Bin Qiu Guonan Chen 《Chirality》2013,25(11):751-756
The preparative‐scale separation of chiral compounds is vitally important for the pharmaceutical industry and related fields. Herein we report a simple approach for rapid preparative separation of enantiomers using functional nucleic acids modified gold nanoparticles (AuNPs). The separation of DL‐tryptophan (DL‐Trp) is demonstrated as an example to show the feasibility of the approach. AuNPs modified with enantioselective aptamers were added into a racemic mixture of DL‐Trp. The aptamer‐specific enantiomer (L‐Trp) binds to the AuNPs surface through aptamer‐L‐Trp interaction. The separation of DL‐Trp is then simply accomplished by centrifugation: the precipitate containing L‐Trp bounded AuNPs is separated from the solution, while the D‐Trp remains in the supernatant. The precipitate is then redispersed in water. The aptamer is denatured under 95 °C and a second centrifugation is then performed, resulting in the separation of AuNPs and L‐Trp. The supernatant is finally collected to obtain pure L‐Trp in water. The results show that the racemic mixture of DL‐Trp is completely separated into D‐Trp and L‐Trp, respectively, after 5 rounds of repeated addition of fresh aptamer‐modified AuNPs to the DL‐Trp mixture solution. Additionally, the aptamer‐modified AuNPs can be repeatedly used for at least eight times without significant loss of its binding ability because the aptamer can be easily denatured and renatured in relatively mild conditions. The proposed approach could be scaled up and extended to the separation of other enantiomers by the adoption of other enantioselective aptamers. Chirality 25:751–756, 2013. © 2013 Wiley Periodicals, Inc. 相似文献
97.
Catherine McLaughlin Marilyn L. Bowman Cheryl L. Bradley 《Chronobiology international》2013,30(2-3):455-470
Seasonal effects on shift‐work tolerance were assessed using the Standardized Shiftwork Index and the 21‐item Hamilton Depression Scale. Participants (N=88) mainly worked a two‐day, two‐night, four‐off rotation with 12 h shifts changing at 06∶00 and 18∶00 h in Vancouver, Canada. At this latitude (~49° N), daylength varies seasonally from ~16 to ~8 h, and both daily commutes occur in the dark in mid‐winter and in sunlight in mid‐summer. Questionnaires were completed twice, near the summer and winter solstices (order counterbalanced). Outcome variables were mood, general psychological health, sleep quality, chronic fatigue, physical health, job satisfaction, and social and domestic disruption. Of these, general psychological health and mood were significantly worse in winter, while sleep was more disturbed in summer. In winter, 31% exceeded the cutoff for psychological distress, and >70% scored in the higher than normal range for depressive symptoms. In summer, the proportions dropped to 19% and 53%, respectively. Measures of physical health and psychosocial well‐being showed no seasonal effects. Relationships among explanatory and outcome variables, assessed by linear regression and canonical correlations, were also stable across season. Neuroticism was the strongest predictor of tolerance to shift work. Age was predictive only of sleep disturbance in both summer and winter. These results indicate that time of year can affect important outcome measures in shift‐work assessment and intervention studies. The high average scores on measures of psychological distress and depression in winter suggest that at northern latitudes, some shift schedules may increase the risk of seasonal‐type depression. 相似文献
98.
Isabelle Côté 《Ethnic and racial studies》2013,36(11):1855-1873
The tumultuous events of summer 2009 have brought Uighur protests and minority mobilization in the Xinjiang Uighur Autonomous Region (XUAR) to the forefront. But this focus overlooks similar protests organized by various groups of Han Chinese settlers over the years. This paper contributes to the body of literature on minority mobilization and ethnic relations in Xinjiang by illustrating how the political mobilization of a group that is simultaneously a national majority and a regional minority differs substantially from ‘traditional’ minority mobilization. Reviewing the main instances of Han Chinese political mobilization since the XUAR was created in 1955, I argue that two factors are particularly important in enabling their mobilization: the Han Chinese's subjective perception of discrimination and their close ethnic ties to the state. This paper concludes with a discussion on the presence of a cycle of protests between Han settlers and the Uighurs in Xinjiang. 相似文献
99.
Kevin W. Riddle 《Ocean Development & International Law》2013,44(3-4):265-297
Illegal, unreported, and unregulated (IUU) Fishing is considered a major threat to high seas fish stocks. Each of the the international regional fishery management organizations (RFMOs) are combating some form of IUU fishing and this led the Food and Agriculture Oranization of the United Nations (FAO) to adopt the International Plan of Action to Deter, Prevent and Eliminate IUU Fishing (IPOA-IUU). This article will analyze the issues involved with IUU fishing, examine the recommendations in the IPOA, and consider examples of successful management and enforcement measures in use by states and RFMOs. Finally, recent developments in China will be viewed as an example of how international cooperation is contagious. 相似文献
100.
RésuméCe travail a pour objectif l’étude de quelques aspects bio-écologiques de la cochenille violette, Parlatoria oleae Colvée 1880, bio-agresseur des cultures de l’Olivier en régions arides. Le suivi du cycle biologique ainsi que la démo-écologie de ce ravageur ont été réalisés grâce à des dénombrements périodiques des populations sur les différents organes de l’arbre (méthodes de Vasseur &; Schvester) de décembre 2010 à décembre 2011 dans la région d’Ain Touta (nord-est algérien). L’espèce y a montré deux générations par an : une génération printanière se développant entre avril et juillet et une génération automnale évoluant entre août et octobre. La ponte débuta en avril et s’échelonna jusqu‘à la fin septembre. L’exposition nord est la plus favorable à cette diaspine qui y trouve des conditions microclimatiques optimales pour son développement. La ponte moyenne est de 8 à 9 ?ufs par femelle. L’analyse statistique de l’effet des conditions climatiques étudiées (températures minimale, maximale et moyenne ; précipitations, gelée et indice d’aridité De Martone) sur les effectifs des différents stades, montre une grande variabilité d’un stade à un autre. L’analyse statistique établie révèle également que les effectifs de l’espèce présentent des variations très hautement significatives selon l’orientation dans l’arbre d’olive colonisé. 相似文献