首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3969篇
  免费   385篇
  国内免费   13篇
  4367篇
  2022年   62篇
  2021年   105篇
  2020年   45篇
  2019年   70篇
  2018年   67篇
  2017年   52篇
  2016年   105篇
  2015年   216篇
  2014年   188篇
  2013年   235篇
  2012年   287篇
  2011年   257篇
  2010年   180篇
  2009年   142篇
  2008年   203篇
  2007年   178篇
  2006年   185篇
  2005年   167篇
  2004年   150篇
  2003年   144篇
  2002年   140篇
  2001年   85篇
  2000年   76篇
  1999年   72篇
  1998年   57篇
  1997年   47篇
  1996年   34篇
  1995年   42篇
  1994年   36篇
  1993年   25篇
  1992年   48篇
  1991年   43篇
  1990年   49篇
  1989年   38篇
  1988年   32篇
  1987年   38篇
  1985年   35篇
  1984年   18篇
  1983年   27篇
  1982年   35篇
  1981年   28篇
  1980年   24篇
  1979年   18篇
  1978年   17篇
  1977年   20篇
  1975年   16篇
  1974年   18篇
  1973年   17篇
  1970年   17篇
  1969年   16篇
排序方式: 共有4367条查询结果,搜索用时 15 毫秒
81.
Role of lipid peroxidation and antioxidative enzymes (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase and glutathione reductase) in water stress-promoted senescence of detached rice leaves was investigated. The senescence was followed by measuring the decrease in protein content. Increased lipid peroxidation was closely correlated with senescence in water stressed leaves. Decrease in superoxide dismutase activity was evident 8 h after beginning of water stress. However, decreased catalase, peroxidase, and ascorbate peroxidase activity was observed only when senescence was observed. Glutathione reductase was not affected by water stress. Free radical scavengers retarded water stress-enhanced senescence.  相似文献   
82.
Grace  D. C.  Diall  O.  Saville  K.  Warboys  D.  Ward  P.  Wild  I.  Perry  B. D. 《EcoHealth》2022,19(3):342-353
EcoHealth - Small farmers produce most food in low- and middle-income countries and most small farmers rely on directly or indirectly working equids (WE). The lack of methods and metrics for...  相似文献   
83.
Coral Reefs - A correction to this paper has been published: https://doi.org/10.1007/s00338-021-02111-z  相似文献   
84.
85.
Background: The association between antihypertensive medications and survival in cancer patients remains unclear. Objectives: To explore the association between classes of antihypertensive drugs and survival in cancer patients. Methods: Provincial Cancer Registry data was linked with a Provincial Drug Program Information Network (DPIN) for patients with lung (n = 4241), colorectal (n = 3967), breast (n = 4019) or prostate (n = 3355) cancer between the years of 2004 and 2008. Cox regression analyses were used to compare survival of patients using beta blockers (BBs), angiotensin-converting enzyme inhibitors/receptor blockers (ACEi/ARB), calcium channel blockers (CCBs) or thiazide diuretics (TDs) to survival of patients who did not use any of these antihypertensive drugs. Survival of patients using only one class of antihypertensive drugs were compared to each other, with BBs as the reference class. Results: Compared to the antihypertensive drug non-user cohort, BBs had no effect on survival for any of the cancers. ACEi/ARBs use was weakly associated with increased deaths for breast cancer (HR: 1.22, 95% CI: 1.04–1.44) and lung cancer (HR: 1.11, 95% CI: 1.03–1.21) patients. Deaths were also increased with CCB use in patients with breast cancer (HR: 1.22, 95% CI: 1.02–1.47) and with TD use in lung cancer patients (HR: 1.1, 95% CI: 1.01–1.19). There was strong evidence (p-value <0.0001) of an increase in deaths with TD use for colorectal (HR: 1.28, 95% CI: 1.15–1.42), and prostate (HR 1.41, 1.2–1.65) cancer patients. When including only antihypertensive drug users prescribed one drug class, lung cancer patients receiving CCBs had improved survival compared to BBs (HR 0.79, 95% CI: 0.64–0.98). Conclusions: Some classes of antihypertensive agents are associated with a decreased survival in certain cancers. The decrease could be due to more comorbidities in antihypertensive drug users. However, CCB use was associated with improved survival in lung cancer patients.  相似文献   
86.
87.
A significantly higher proportion of female hamsters developed tumors than did males given the same dose of adenovirus-12 (Huie) at birth over a dose range from 10(5.0) to 10(7.0)tcd(50) for human embryonic kidney cells. The 50% tumor dose (td(50)) was calculated to be 10(5.90)tcd(50) for females and 10(6.27) for males. Tumor response patterns induced with approximate td(50) inocula, 10(6.0) for females and 10(6.3) for males, were quite similar. The greater susceptibility of females was not found to be characteristic of a single strain of hamsters; nor was it attributable to a single lot of virus, to a single type of human cell used to produce the virus, nor to the degree of purification of the virus inoculum. The inoculation route did not appear to be of importance. Inasmuch as the foregoing extrinsic factors were of little influence, it was concluded that the mechanism is host-mediated, presumably hormonally controlled. The possibility that female cells, independent of host control, are more susceptible to adenovirus-12 oncogenesis than male cells has not been explored. Tumor regression occurred in 20% of the 211 tumors in males and in 15% of the 355 tumors in females. Adenovirus-12 T-antibody was detected in all but six of 473 sera tested from tumor-bearing hamsters and in 50% of 94 sera tested from non-tumor-bearing animals given virus at birth. Antibodies in the latter group were detected almost exclusively by indirect immunofluorescence. This technique appears to be extremely sensitive for detection of low levels of adeno-12 T-antibodies. The implications of T-antibody in nontumor-bearing virus-injected hamsters are discussed. Sera from normal hamsters were free of T-antibody.  相似文献   
88.
89.
Chen YH  Chao YY  Hsu YY  Hong CY  Kao CH 《Plant cell reports》2012,31(6):1085-1091
Lateral root (LR) development performs the essential tasks of providing water, nutrients, and physical support to plants. Therefore, understanding the regulation of LR development is of agronomic importance. In this study, we examined the effect of nitric oxide (NO), auxin, and hemin (Hm) on LR formation in rice. Treatment with Hm [a highly effective heme oxygenase (HO) inducer], sodium nitroprusside (SNP, an NO donor), or indole-3-butyric acid (IBA, a naturally occurring auxin) induced LR formation and HO activity. LR formation and HO activity induced by SNP and IBA but not Hm was reduced by the specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. As well, Hm, SNP, and IBA could induce OsHO1 mRNA expression. Zn protoporphyrin IX (the specific inhibitor of HO) and hemoglobin (the carbon monoxide/NO scavenger) reduced LR number and HO activity induced by Hm, SNP, and IBA. Our data suggest that HO is required for Hm-, auxin-, and NO-induced LR formation in rice.  相似文献   
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号