全文获取类型
收费全文 | 32135篇 |
免费 | 2671篇 |
国内免费 | 3850篇 |
专业分类
38656篇 |
出版年
2024年 | 127篇 |
2023年 | 700篇 |
2022年 | 848篇 |
2021年 | 1004篇 |
2020年 | 1088篇 |
2019年 | 1445篇 |
2018年 | 1139篇 |
2017年 | 1190篇 |
2016年 | 1244篇 |
2015年 | 1311篇 |
2014年 | 1716篇 |
2013年 | 2269篇 |
2012年 | 1303篇 |
2011年 | 1560篇 |
2010年 | 1271篇 |
2009年 | 1666篇 |
2008年 | 1730篇 |
2007年 | 1729篇 |
2006年 | 1615篇 |
2005年 | 1481篇 |
2004年 | 1307篇 |
2003年 | 1163篇 |
2002年 | 1056篇 |
2001年 | 842篇 |
2000年 | 716篇 |
1999年 | 766篇 |
1998年 | 609篇 |
1997年 | 569篇 |
1996年 | 512篇 |
1995年 | 518篇 |
1994年 | 499篇 |
1993年 | 385篇 |
1992年 | 357篇 |
1991年 | 351篇 |
1990年 | 285篇 |
1989年 | 257篇 |
1988年 | 233篇 |
1987年 | 230篇 |
1986年 | 177篇 |
1985年 | 203篇 |
1984年 | 216篇 |
1983年 | 148篇 |
1982年 | 176篇 |
1981年 | 125篇 |
1980年 | 122篇 |
1979年 | 109篇 |
1978年 | 86篇 |
1977年 | 50篇 |
1976年 | 44篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
C.M. Turkelson T.E. Solomon L. Bussjaeger J. Turkelson M. Ronk J.E. Shively F.J. Ho J.R. Reeve Jr 《Peptides》1988,9(6):1255-1260
Cholecystokinin-58 (CCK-58) was purified from rat intestines using an extraction method that yields large amounts of this peptide. Greater than 30% of total CCK immunoreactivity eluted before CCK-39 upon gel permeation chromatography (Sephadex G-50) if extracts were loaded onto Sep Pak cartridges before freezing. If the extracts were frozen and stored at −70°C for six weeks, only 20% of the material eluted in this region and total immunoreactivity was reduced by 50%, suggesting that proteases were active under these storage conditions. This early eluting peak was purified by reverse phase and ion-exchange HPLC to a single absorbance peak. Microsequence analysis of this peak detected AVLRPDSEP which is the amino terminus of rat CCK-58 predicted from the rat preprocholecystokinin cDNA. Because degradation of CCK-58 occurred in these extracts, it is possible that CCK-58 is the predominant molecule form in the rat small intestine. 相似文献
993.
Abstract We have isolated a set of Tn 10 -generated deletions starting from the distal end of the ompR envZ operon of Escherichia coli K12. Most of the deletions removed both ompR and envZ genes or ended in ompR . These deletions exhibited an OmpC− OmpF− phenotype. One deletion removed only part of envZ and the strain was phenotypically OmpC− OmpF+/− . This deletion of the distal part of envZ did not affect osmoregulation of ompC . However, ompF osmoregulation appeared reversed. High osmolarity in the growth medium resulted in production of OmpF close to the wild-type level. 相似文献
994.
995.
禺毛茛及其复合体种间亲缘关系形成研究 总被引:1,自引:1,他引:0
在Tamura M.,Okada及廖亮研究的基础上,通过禺毛茛复合体(禺毛茛R.cantoniensis 4x,卷喙毛茛R.sileri folius var.silerifolius 2x,长花毛茛R.sileri folius var.dolicathus 2x,茴茴蒜R.chinensis 2x,扬子毛茛R.sieboldii 6x及8x)的核型分析,结合地球环境的演变历史,进一步研究了禺毛茛的形成方式和时间,并对禺毛茛复合体种间亲缘关系的形成进行了探讨,为毛茛属系统进化研究提供资料。 相似文献
996.
濒危平胸龟两个自然居群的ISSR分析 总被引:3,自引:0,他引:3
利用22个ISSR引物研究了28个来自广东从化居群和21个来自福建寿宁居群的野生平胸龟(Platysternon megacephalum)的遗传多样性。结果表明,分布于这两个地区的平胸龟总居群和居群内均具有较高的遗传多样性,而广东从化居群遗传多样性高于福建寿宁居群。居群间的遗传变异度FST=0.3715(P<0.001),遗传分化系数Gst为0.2059。NJ树聚类分析显示,广东从化居群和福建寿宁居群各自聚成两个类群,有较明显的居群分化,具有一定的地理区域性,但基因流Nm为1.9279,这表明平胸龟两自然居群间存在一定基因流。此外,结合BSA技术,从11条引物中筛选出11个可作为鉴别广东从化居群或福建寿宁居群的分子标记。 相似文献
997.
998.
Franc García Xavi Schelling Julen Castellano Andrs Martín-García Francesc Pla Jairo Vzquez-Guerrero 《Biology of sport / Institute of Sport》2022,39(2):237
The purpose of this study was to compare physical demands during the most demanding scenarios (MDS) of different training sessions and official matches in professional basketball players across playing positions. Thirteen professional basketball players were monitored over a 9-week competitive season using a local positioning system. Peak physical demands included total distance, distance covered at > 18 km·h-1, distance and number of accelerations (≥ 2 m∙s-2) and decelerations (≤ -2 m∙s-2) over a 60-second epoch. Analysis of variance for repeated measures, Bonferroni post-hoc tests and standardised Cohen’s effect size (ES) were calculated. Overall, almost all physical demands during the MDS of training were lower (-6.2% to -35.4%) compared to official matches. The only variable that surpassed competition demands was distance covered at > 18 km·h-1, which presented moderate (ES = 0.61, p = 0.01) and small (ES = 0.48, p > 0.05) increases during training sessions four and three days before a competition, respectively. Conversely, the two previous practices before match day presented trivial to very large decreases (ES = 0.09–2.66) in all physical demands. Furthermore, centres achieved the lowest peak value in total distance covered during matches, forwards completed the greatest peak distance at > 18 km·h-1, and guards performed the greatest distance and number of high-intensity accelerations and decelerations. In conclusion, physical demands during the MDS of different training sessions across the microcycle failed to match or surpass peak values during official matches, which should be considered when prescribing a training process intended to optimise the MDS of match play. 相似文献
999.
Jos M. Oliva-Lozano Carlos D. Gmez-Carmona Víctor Fortes Jos Pino-Ortega 《Biology of sport / Institute of Sport》2022,39(2):397
The aims of this study were to: (a) describe and compare the volume and intensity from the workload of professional soccer players between training and MD, and (b) analyse the effect that the length of the microcycle had on the workload. A cohort study was designed for a full season in La Liga 123. Wearable tracking systems collected the distance covered in meters (m), total number of high-intensity accelerations (ACCHIGH) and decelerations (DECHIGH), total number of high-speed running actions (HSRA), high-speed running distance (HSRD), high metabolic load distance (HMLD), and player load (PL) from training days (MD+1, MD-4, MD-3, MD-2, and MD-1) and MD. Significant differences were found between training and MD workload, MD workload being the most demanding for all intensity and volume variables (F = 36.35–753.94; p < 0.01; wp2 = 0.21–0.85). The greatest training intensity and volume were found on MD-4 and MD-3 (p < 0.05). In addition, a novel finding was that the length of the microcycle had a significant effect on the workload both in volume and intensity (F = 4.84–14.19; p < 0.01; wp2 = 0.03–0.09), except for relative ACCHIGH, DECHIGH, and HMLD. Although MD-4 and MD-3 were the most suitable days for loading the players, the results showed that MD elicited a unique stimulus in terms of volume and intensity. Consequently, coaches need to include specific training drills to adapt the players for the competitive demands. Finally, special focus should be placed on MD from short and regular microcycles (5-day, 6-day, or 7-day microcycles) since declines in physical performance were observed in comparison with long microcycles (8-day or 9-day microcycles). 相似文献
1000.