全文获取类型
收费全文 | 113355篇 |
免费 | 9668篇 |
国内免费 | 4328篇 |
出版年
2023年 | 865篇 |
2022年 | 973篇 |
2021年 | 3599篇 |
2020年 | 2628篇 |
2019年 | 3211篇 |
2018年 | 3493篇 |
2017年 | 2715篇 |
2016年 | 4132篇 |
2015年 | 6192篇 |
2014年 | 7231篇 |
2013年 | 7856篇 |
2012年 | 9673篇 |
2011年 | 8966篇 |
2010年 | 5589篇 |
2009年 | 4989篇 |
2008年 | 6361篇 |
2007年 | 5844篇 |
2006年 | 5186篇 |
2005年 | 4526篇 |
2004年 | 4159篇 |
2003年 | 3773篇 |
2002年 | 3100篇 |
2001年 | 2597篇 |
2000年 | 2477篇 |
1999年 | 2034篇 |
1998年 | 1030篇 |
1997年 | 910篇 |
1996年 | 878篇 |
1995年 | 832篇 |
1994年 | 745篇 |
1993年 | 642篇 |
1992年 | 1113篇 |
1991年 | 878篇 |
1990年 | 788篇 |
1989年 | 762篇 |
1988年 | 641篇 |
1987年 | 594篇 |
1986年 | 512篇 |
1985年 | 502篇 |
1984年 | 401篇 |
1983年 | 361篇 |
1982年 | 280篇 |
1981年 | 221篇 |
1980年 | 225篇 |
1979年 | 300篇 |
1978年 | 254篇 |
1977年 | 232篇 |
1976年 | 238篇 |
1974年 | 255篇 |
1972年 | 213篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
5.
6.
Ronac Mamtani James D. Lewis Frank I. Scott Tariq Ahmad David S. Goldberg Jashodeep Datta Yu-Xiao Yang Ben Boursi 《PLoS medicine》2016,13(4)
BackgroundSeveral prior studies have found an association between statin use and reduced risk of colorectal cancer. We hypothesized that these findings may be due to systematic bias and examined the independent association of colorectal cancer risk with statin use, serum cholesterol, and change in cholesterol concentration.ConclusionsAlthough the risk of colorectal cancer was lower in statin users versus nonusers, no difference was observed among those who continued versus discontinued statin therapy, suggesting the potential for indication bias. The association between decreased serum cholesterol and colorectal cancer risk suggests a cholesterol-lowering effect of undiagnosed malignancy. Clinical judgment should be used when considering causes of cholesterol reduction in patients, including those on statin therapy. 相似文献
7.
So Jeong Park Doo Ri Park Deepak Bhattarai Kyeong Lee Jaesang Kim Yun Soo Bae Soo Young Lee 《Molecules and cells》2014,37(8):628-635
2-(Trimethylammonium) ethyl (R)-3-methoxy-3-oxo-2-stearamidopropyl phosphate [(R)-TEMOSPho], a derivative of an organic chemical identified from a natural product library, promotes highly efficient megakaryopoiesis. Here, we show that (R)-TEMOSPho blocks osteoclast maturation from progenitor cells of hematopoietic origin, as well as blocking the resorptive function of mature osteoclasts. The inhibitory effect of (R)-TEMOSPho on osteoclasts was due to a disruption of the actin cytoskeleton, resulting from impaired downstream signaling of c-Fms, a receptor for macrophage-colony stimulating factor linked to c-Cbl, phosphoinositol-3-kinase (PI3K), Vav3, and Rac1. In addition, (R)-TEMOSPho blocked inflammation-induced bone destruction by reducing the numbers of osteoclasts produced in mice. Thus, (R)-TEMOSPho may represent a promising new class of antiresorptive drugs for the treatment of bone loss associated with increased osteoclast maturation and activity. 相似文献
8.
En-Chi Chiu Shu-Chun Lee Chian-Jue Kuo For-Wey Lung I-Ping Hsueh Ching-Lin Hsieh 《PloS one》2015,10(11)
A performance-based measure for assessing executive functions (EF) is useful to understand patients’ real life performance of EF. This study aimed to develop a performance-based measure of executive functions (PEF) based on the Lezak model and to examine psychometric properties (i.e., unidimensionality and reliability) of the PEF using Rasch analysis in patients with schizophrenia. We developed the PEF in three phases: (1) designing the preliminary version of PEF; (2) consultation with experts, cognitive interviews with patients, and pilot tests on patients to revise the preliminary PEF; (3) establishment of the final version of the PEF and examination of unidimensionality and Rasch reliability. Two hundred patients were assessed using the revised PEF. After deleting items which did not satisfy the Rasch model’s expectations, the final version of the PEF contained 1 practice item and 13 test items for assessing the four domains of EF (i.e., volition, planning, purposive action, and effective performance). For unidimensional and multidimensional Rasch analyses, the 4 domains showed good reliability (i.e., 0.77–0.85 and 0.87–0.90, respectively). Our results showed that the PEF had satisfactory unidimensionality and Rasch reliability. Therefore, clinicians and researchers could use the PEF to assess the four domains of EF in patients with schizophrenia. 相似文献
9.
There is evidence that telomere length (TL), telomerase activity (TA), and age are related to the replicative potential of human nucleus pulposus chondrocytes (NPCs). However, it has not yet been established if any of these factors can serve as predictors of the replicative potential of NPCs. To establish predictors of the replicative potential of NPCs, we evaluated potential relationships between replicative capacity of NPCs, initial TL (telomere length at the first passage), initial TA (telomerase activity at the first passage), and age. Nucleus pulposus specimens were obtained from 14 patients of various ages undergoing discectomy. NPCs were serially cultivated until the end of their replicative lifespans. Relationships among cumulative population doubling level (PDL), initial TL, initial TA, and age were analyzed. Initial TA was negatively correlated with age (r = -0.674, P = 0.008). However, no correlation between initial TL and age was observed. Cumulative PDL was also negatively correlated with age (r = -0.585, P = 0.028). Although the cumulative PDL appeared to increase with initial TL or initial TA, this trend was not statistically significant. In conclusion, age is the sole predictor of the replicative potential of human NPCs, and replicative potential decreases with age. Initial TL and initial TA are not predictors of replicative potential, and can serve only as reference values. 相似文献
10.