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   16453篇
  免费   1364篇
  国内免费   37篇
电工技术   208篇
综合类   22篇
化学工业   3553篇
金属工艺   642篇
机械仪表   964篇
建筑科学   382篇
矿业工程   11篇
能源动力   648篇
轻工业   1639篇
水利工程   51篇
石油天然气   22篇
无线电   2634篇
一般工业技术   3601篇
冶金工业   1628篇
原子能技术   231篇
自动化技术   1618篇
  2023年   172篇
  2022年   109篇
  2021年   479篇
  2020年   392篇
  2019年   441篇
  2018年   530篇
  2017年   540篇
  2016年   644篇
  2015年   546篇
  2014年   768篇
  2013年   1142篇
  2012年   1073篇
  2011年   1295篇
  2010年   957篇
  2009年   960篇
  2008年   864篇
  2007年   641篇
  2006年   568篇
  2005年   508篇
  2004年   481篇
  2003年   437篇
  2002年   398篇
  2001年   286篇
  2000年   251篇
  1999年   245篇
  1998年   539篇
  1997年   384篇
  1996年   250篇
  1995年   210篇
  1994年   189篇
  1993年   181篇
  1992年   135篇
  1991年   106篇
  1990年   106篇
  1989年   101篇
  1988年   75篇
  1987年   60篇
  1986年   63篇
  1985年   82篇
  1984年   72篇
  1983年   49篇
  1982年   43篇
  1981年   45篇
  1980年   44篇
  1979年   39篇
  1978年   34篇
  1977年   51篇
  1976年   80篇
  1975年   41篇
  1973年   32篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Coptidis Rhizoma is the dried rhizome from the Coptis chinensis Franch. that has been shown to have a number of beneficial pharmacological properties including antioxidant, anti-inflammatory, and anti-cancer effects. However, the anti-cancer effects of Coptidis Rhizoma on hepatocellular carcinoma (HCC) remain unclear. In this study, we investigated the anti-cancer properties of Coptidis Rhizoma ethanol extract (CR) in HCC Hep3B cells and in a xenograft mouse model. Our results showed that the CR significantly inhibited cell growth and induced apoptosis in Hep3B cells through increased expression of Bcl-2 associated x-protein (Bax) and cleavage of poly-ADP ribose polymerase (PARP), reduced expression of Bcl-2, and activated caspases. CR also increased the generation of intracellular reactive oxygen species (ROS), which caused a loss of mitochondrial membrane potential (MMP, ΔΨm) and activation of the mitochondria-mediated intrinsic apoptosis pathway. Moreover, N-acetylcysteine (NAC), a ROS inhibitor, markedly blocked the effects of CR on apoptotic pathways. CR also induced the expression of light chain 3 (LC3)-I/II, a key autophagy regulator, whereas CR-mediated autophagy was significantly suppressed by NAC. In addition, pre-treatment with NAC perfectly attenuated the inhibition of cell invasion and migration of CR-stimulated Hep3B cells. Furthermore, oral administration of CR suppressed Hep3B tumor growth in xenograft mice without toxicity, alterations to body weight, or changes in hematological and biochemical profiles. Taken together, our findings suggest that CR has anti-tumor effects that result from ROS generation, and may be a potential pharmacological intervention for HCC.  相似文献   
2.
A strategy for creating potent and pan-genotypic stimulator of interferon genes (STING) agonists is described. Locking a bioactive U-shaped conformation of cyclic dinucleotides by introducing a transannular macrocyclic bridge between the nucleic acid bases leads to a topologically novel macrocycle-bridged STING agonist (MBSA). In addition to substantially enhanced potency, the newly designed MBSAs, exemplified by clinical candidate E7766 , exhibit broad pan-genotypic activity in all major human STING variants. E7766 is shown to have potent antitumor activity with long lasting immune memory response in a mouse liver metastatic tumor model. Two complementary stereoselective synthetic routes to E7766 are also described.  相似文献   
3.
With the rapid growth of wireless communication devices, the influences of electromagnetic fields (EMF) on human health are gathering increasing attention. Since the skin is the largest organ of the body and is located at the outermost layer, it is considered a major target for the health effects of EMF. Skin pigmentation represents one of the most frequent symptoms caused by various non-ionizing radiations, including ultraviolet radiation, blue light, infrared, and extremely low frequency (ELF). Here, we investigated the effects of EMFs with long-term evolution (LTE, 1.762 GHz) and 5G (28 GHz) bandwidth on skin pigmentation in vitro. Murine and Human melanoma cells (B16F10 and MNT-1) were exposed to either LTE or 5G for 4 h per day, which is considered the upper bound of average smartphone use time. It was shown that neither LTE nor 5G exposure induced significant effects on cell viability or pigmentation. The dendrites of MNT-1 were neither lengthened nor regressed after EMF exposure. Skin pigmentation effects of EMFs were further examined in the human keratinocyte cell line (MNT-1-HaCaT) co-culture system, which confirmed the absence of significant hyper-pigmentation effects of LTE and 5G EMFs. Lastly, MelanoDerm™, a 3D pigmented human epidermis model, was irradiated with LTE (1.762 GHz) or 5G (28 GHz), and image analysis and special staining were performed. No changes in the brightness of MelanoDerm™ tissues were observed in LTE- or 5G-exposed tissues, except for only minimal changes in the size of melanocytes. Collectively, these results imply that exposure to LTE and 5G EMFs may not affect melanin synthesis or skin pigmentation under normal smartphone use condition.  相似文献   
4.
Amyloid precursor protein (APP) is a type 1 transmembrane glycoprotein, and its homologs amyloid precursor-like protein 1 (APLP1) and amyloid precursor-like protein 2 (APLP2) are highly conserved in mammals. APP and APLP are known to be intimately involved in the pathogenesis and progression of Alzheimer’s disease and to play important roles in neuronal homeostasis and development and neural transmission. APP and APLP are also expressed in non-neuronal tissues and are overexpressed in cancer cells. Furthermore, research indicates they are involved in several cancers. In this review, we examine the biological characteristics of APP-related family members and their roles in cancer.  相似文献   
5.
The positive effects of a lithiophilic substrate on the electrochemical performance of lithium metal anodes are confirmed in several reports, while the understanding of lithiophilic substrate-guided lithium metal nucleation and growth behavior is still insufficient. In this study, the effect of a lithiophilic surface on lithium metal nucleation and growth behaviors is investigated using a large-area Ti3C2Tx MXene substrate with a large number of oxygen and fluorine dual heteroatoms. The use of the MXene substrate results in a high lithium-ion concentration as well as the formation of uniform solid–electrolyte-interface (SEI) layers on the lithiophilic surface. The solid–solid interface (MXene-SEI layer) significantly affects the surface tension of the deposited lithium metal nuclei as well as the nucleation overpotential, resulting in the formation of uniformly dispersed lithium nanoparticles ( ≈ 10–20 nm in diameter) over the entire MXene surface. The primary lithium nanoparticles preferentially coalesce and agglomerate into larger secondary particles while retaining their primary particle shapes. Subsequently, they form close-packed structures, resulting in a dense metal layer composed of particle-by-particle microstructures. This distinctive lithium metal deposition behavior leads to highly reversible cycling performance with high Columbic efficiencies >  99.0% and long cycle lives of over 1000 cycles.  相似文献   
6.
7.
Food Science and Biotechnology - A new analytical method was developed for the simultaneous determination of seven food additives (Ponceau 4R, Allura Red AC, Amaranth, 4-hydroxymethyl benzoic acid,...  相似文献   
8.
Chun  Dong Hyun  Rhim  Geun Bae  Youn  Min Hye  Deviana  Deviana  Lee  Ji Eun  Park  Ji Chan  Jeong  Heondo 《Topics in Catalysis》2020,63(9-10):793-809
Topics in Catalysis - Fischer–Tropsch synthesis (FTS) is a promising way to produce clean liquid fuels and high value-added chemicals from low-value carbon-containing resources such as coal,...  相似文献   
9.

Smart manufacturing system must be designed based on a set of strategic objectives and a variety of surrounding environments; therefore, it includes a series of complex decisions and trade-offs between investment and profit. The MSDD based on the axiomatic design principle has an advantage on breaking down requirements and parameters and considering the relationships of them, but there is a limit to quantify relative weights of each requirement and parameter. To complement the limitation, a quantification method applying the analytic network process is proposed. The proposed method can calculate the relative importance degrees of the requirement and parameter objectively and help us understand and focus on more important factors of the smart manufacturing system design.

  相似文献   
10.
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