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   1420篇
  免费   85篇
  国内免费   8篇
  2023年   9篇
  2022年   5篇
  2021年   42篇
  2020年   25篇
  2019年   31篇
  2018年   49篇
  2017年   40篇
  2016年   52篇
  2015年   82篇
  2014年   101篇
  2013年   92篇
  2012年   137篇
  2011年   116篇
  2010年   91篇
  2009年   62篇
  2008年   71篇
  2007年   79篇
  2006年   69篇
  2005年   63篇
  2004年   41篇
  2003年   36篇
  2002年   34篇
  2001年   28篇
  2000年   35篇
  1999年   20篇
  1998年   17篇
  1997年   9篇
  1996年   13篇
  1995年   4篇
  1994年   2篇
  1993年   1篇
  1992年   6篇
  1991年   7篇
  1990年   6篇
  1989年   3篇
  1988年   6篇
  1987年   3篇
  1986年   1篇
  1984年   2篇
  1983年   3篇
  1981年   2篇
  1980年   3篇
  1977年   3篇
  1975年   2篇
  1974年   3篇
  1973年   1篇
  1972年   1篇
  1968年   2篇
  1922年   1篇
  1899年   1篇
排序方式: 共有1513条查询结果,搜索用时 15 毫秒
991.
Tremendous efforts have been invested in the development of the internet of things during the past 10 years. Implantable sensors still need embedded miniaturized energy harvesting devices, since commercialized thin films and microbatteries do not provide sufficient power densities and suffer from limited lifetime. Therefore, micro‐supercapacitors are good candidates to store energy and deliver power pulses while providing non‐constant voltage output with time. However, multistep expensive protocols involving mask aligners and sophisticated cleanrooms are used to prepare these devices. Here, a simple and versatile laser‐writing procedure to integrate flexible micro‐supercapacitors and microbatteries on current‐collector‐free polyimide foils is reported, starting from commercial powders. Ruthenium oxide (RuO2)‐based micro‐supercapacitors are prepared by laser irradiation of a bilayered tetrachloroauric acid (HAuCl4 · 3H2O)–cellulose acetate/RuO2 film deposited by spin‐coating, which leads to adherent Au/RuO2 electrodes with a unique pillar morphology. The as‐prepared microdevices deliver 27 mF cm?2/540 F cm?3 in 1 m H2SO4 and retain 80% of the initial capacitance after 10 000 cycles. This simple process is applied to make carbon‐based micro‐supercapacitors, as well as metal oxide based pseudocapacitors and battery electrodes, thus offering a straightforward solution to prepare low‐cost flexible microdevices at a large scale.  相似文献   
992.
To be a thinner and more lightweight lithium‐ion battery with high energy density, the next‐generation anode with high gravimetric and volumetric capacity is a prerequisite. In this regard, utilizing high silicon (3579 mAh g?1) content in the electrode for the anode has been highlighted as a practically relevant approach. However, there still remains a crucial issue related to intrinsic volume expansion (>300%) of silicon upon lithiation, which can directly affect severe electrode swelling as well as accelerate its capacity fading by triggering structural degradation and electrical contact loss between particles. Herein, macropore‐exploited design, which can accommodate the volume change of high silicon content within the extended pore of graphite upon repeated cycling, is introduced. Such unique macropore‐exploited design leads to much less electrode swelling, by preserving its morphological integrity and contact between particles, than that of the comparative group with different sized pore and silicon distribution. As a result, this anode (914 mAh g?1) demonstrates notable gravimetric (220 Wh kg?1 at 6000 W kg?1) and volumetric energy density (623 Wh L?1 upon full lithiation after 100 cycles), exceeding that of a nano‐silicon blended graphite anode (127 Wh kg?1 and 229 Wh L?1) in the full‐cell system.  相似文献   
993.
Molecular Biology Reports - Malignant melanoma is a very aggressive and serious type of cutaneous cancer. Previous studies indicated the anti-cancer activity of aqueous extract of Moringa oleifera...  相似文献   
994.
The percent weight gain (PWG) and feed efficiency (FE) of Epinephelus coioides were calculated, and the lactobacilli and total microbiota in the posterior intestines, and non-specific immune parameters of grouper, and its susceptibility to Streptococcus sp. and an iridovirus were determined when the fish were fed diets containing Lactobacillus plantarum at 0 (control), 106, 108, or 1010 colony-forming units (cfu) kg?1 for 4 weeks. Results showed that grouper fed a diet containing L. plantarum at the levels of 106, 108, and 1010 cfu kg?1 had significantly increased PGW and FE especially at 108 cfu kg?1 group which were 404.6% and 1.26, respectively. L. plantarum significantly increased in the fish posterior intestines during the L. plantarum feeding period, but decreased rapidly from the intestine within 1 week after changing to the control diet (without L. plantarum). Fish fed a diet containing L. plantarum at 106 and 108 cfu kg?1 had significantly higher survival rates than those fed the control diet after challenge with Streptococcus sp., as well as those fed 108 cfu kg?1 after challenge with an iridovirus, causing increases in the survival rates of 23.3%, 20.0%, and 36.7%, respectively, compared to the control group. The alternative complement activity (ACH50) level of fish fed diets containing L. plantarum after 4 weeks was significantly higher than that of fish fed the control diet, and that of the 108 cfu kg?1 group was significantly higher than those of the 106 and 1010 cfu kg?1 groups, which increased by 83.4% compared to the control group. The lysozyme activity and glutathione peroxidase (GPx) activity of fish fed the L. plantarum-containing diets at 108 and 1010 cfu kg?1 significantly increased compared to those fed the 106 cfu kg?1 L. plantarum diet and control diet, and had increased by 76.3% and 136.6%, and 57.1% and 113.3%, respectively, compared to those fed the control diet. The phagocytic activity (PA), phagocytic index (PI), and respiratory bursts of head kidney leucocytes of fish fed 106, 108, and 1010 cfu kg?1 L. plantarum diets were significantly higher than those of fish fed the control diet after 4 weeks of feeding, and increased 2.2-, 2.2-, and 2.3-fold; 1.8-, 1.8-, and 2.0-fold; and 1.4-, 1.4-, and 1.4-fold, respectively, compared to the control group. We therefore recommend dietary L. plantarum administration at 108 cfu kg?1 to promote growth and enhance immunity and resistance against Streptococcus sp. and an iridovirus of E. coioides.  相似文献   
995.
996.
Tumour necrosis factor alpha (TNF-alpha) has been shown to be the principal mediator of Gram-negative bacterial endotoxin-induced shock. Nevertheless, evidence suggests that TNF-alpha plays a beneficial role in controlling bacterial infections when multiplication of the microorganism is required to kill the host. Using an infant rat model of Neisseria meningitidis infection, we found that blood TNF-alpha concentration reaches a peak three hours after intraperitoneal injection of 3 x 10(6) bacteria. Thereafter, the level of TNF-alpha decreased and was undetectable six to eight hours after infection. A correlation was observed between the magnitude of initial TNF-alpha response and a fatal outcome. Pretreatment of the animals with polyclonal anti-TNF antiserum significantly reduced mortality relative to animals pretreated with control serum. However, pretreatment of animals with anti-TNF antibody did not alter the bacterial invasion of the cerebrospinal fluid. Injection of heat-killed bacteria did not cause death and induced lower TNF-alpha levels than the same number of live bacteria. This excludes the possibility that the role of TNF-alpha is to mediate a shock induced by the endotoxin component of the bacterial inoculum. These results indicate that TNF-alpha has a deleterious effect in this model of bacteraemia. Identification of the critical factors that determine the action of TNF-alpha during lethal bacteraemia will lead to a better understanding of these diseases and the development of appropriate therapeutic intervention.  相似文献   
997.
Lung cancer is the most common cause of cancer death worldwide. Smoking is known as the strongest single factor in the development of lung cancer. However, there are inherited genetic factors that cause different responses to cigarette smoking exposure among individuals. We tried to identify these differences in heavy smokers by examining copy number variations (CNVs) between lung cancer patients and healthy controls. Analysis by array comparative genomic hybridization which was tested with 20-person training set (10 lung cancer patients, 10 healthy controls) showed 26 significant (adjusted P < 0.05) clones with either copy number gains or losses. Three genes, KCTD11, FGF11, and PTPRH on chromosomal regions 17p13.1 (KCTD11 and FGF11) and 19q13.42 (PTPRH), were selected (adjusted P < 0.001) and tested by real-time quantitative PCR with 34 healthy controls and 54 lung cancer patients. KCTD11 on the chromosomal region 17p13.1 showed significant high odds ratio (OR = 16.0) in heavy smokers, implying that this is a susceptibility region for lung cancer in this group. Therefore, CNVs of 17p13.1 is a promising candidate to identify individuals with a high genetic risk for the development of lung cancer.  相似文献   
998.
Subedi KP  Kim JC  Kang M  Son MJ  Kim YS  Woo SH 《Cell calcium》2011,49(2):136-143
Voltage-dependent anion channels (VDACs) are pore forming proteins predominantly found in the outer mitochondrial membrane and are thought to transport Ca(2+). In this study, we have investigated the possible role of type 2 VDAC (VDAC2) in cardiac Ca(2+) signaling and Ca(2+) sparks using a lentiviral knock-down (KD) technique and two-dimensional confocal Ca(2+) imaging in immortalized autorhythmic adult atrial cells, HL-1. We confirmed high expression of VDAC2 protein in ventricular, atrial, and HL-1 cells using Western blot analysis. Infection of HL-1 cells with VDAC2-targeting lentivirus reduced the level of VDAC2 protein to ~10%. Comparisons of autorhythmic Ca(2+) transients between wild-type (WT) and VDAC2 KD cells showed no significant change in the magnitude, decay, and beating rate of the Ca(2+) transients. Caffeine (10mM)-induced Ca(2+) release, which indicates sarcoplasmic reticulum (SR) Ca(2+) content, was not altered by VDAC2 KD. Interestingly, however, the intensity, width, and duration of the individual Ca(2+) sparks were significantly increased by VDAC2 KD in resting conditions, with no change in the frequency of sparks. VDAC2 KD significantly delayed mitochondrial Ca(2+) uptake during artificial Ca(2+) pulses in permeabilized HL-1 cells. These results suggest that VDAC2 may facilitate mitochondrial Ca(2+) uptake and restrict Ca(2+) spark expansion without regulating activations of sparks under resting conditions, thereby providing evidence on the functional role of VDAC2 in cardiac local Ca(2+) signaling.  相似文献   
999.
Oxidative stress, glutamate excitotoxicity, and inflammation are the important pathological mechanisms in neurodegenerative diseases. Recently, we reported that 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride protects rat glial cells against glutamate-induced excitotoxicity. In this study, we report the effects of 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride on primary cultured cortical astrocytes after exposure to hydrogen peroxide (H2O2). Pretreatment of cells with 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride prior to H2O2 exposure attenuated the H2O2-induced reductions in cell survival and superoxide dismutase, catalase, glutathione, and glutathione peroxidase activities. It also reduced H2O2-induced increases in reactive oxygen species levels, malondialdehyde content, and production of nitric oxide. These effects were all concentration-dependent. Our results suggest that 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride protects against oxidative stress.  相似文献   
1000.
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