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   4362篇
  免费   334篇
  国内免费   10篇
电工技术   50篇
综合类   5篇
化学工业   847篇
金属工艺   218篇
机械仪表   315篇
建筑科学   55篇
能源动力   158篇
轻工业   357篇
水利工程   17篇
石油天然气   2篇
无线电   852篇
一般工业技术   957篇
冶金工业   286篇
原子能技术   61篇
自动化技术   526篇
  2024年   5篇
  2023年   69篇
  2022年   87篇
  2021年   135篇
  2020年   102篇
  2019年   114篇
  2018年   171篇
  2017年   148篇
  2016年   164篇
  2015年   126篇
  2014年   229篇
  2013年   301篇
  2012年   285篇
  2011年   343篇
  2010年   229篇
  2009年   274篇
  2008年   221篇
  2007年   199篇
  2006年   198篇
  2005年   156篇
  2004年   146篇
  2003年   131篇
  2002年   118篇
  2001年   105篇
  2000年   71篇
  1999年   68篇
  1998年   133篇
  1997年   71篇
  1996年   60篇
  1995年   43篇
  1994年   40篇
  1993年   33篇
  1992年   23篇
  1991年   9篇
  1990年   16篇
  1989年   14篇
  1988年   8篇
  1987年   14篇
  1986年   12篇
  1985年   4篇
  1984年   11篇
  1983年   5篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1973年   2篇
排序方式: 共有4706条查询结果,搜索用时 15 毫秒
971.
Despite their significant economic benefits, wet processes are rarely adopted in optoelectronics industries because of their inherent difficulties in producing high-quality functional films compared with dry processes. Unlike other conventional wet processes, spin-spraying promotes surficial heteronucleation by continuously providing fresh source ions onto the substrate surface and removing excess ions left after nucleation from the surface. Surficial heteronucleation ensures the formation of high-quality films with dense microstructures that are comparable to those obtained by dry processes. This study describes a novel spin-spraying method for growing Ga-doped ZnO (Ga:ZnO) films on glass substrates. The optimum Ga doping concentration of the spin-sprayed Ga:ZnO (SSedGZO) films was determined from the electrical and optical properties of the films. Further, the feasibility of employing UV laser patterning to produce patterned SSedGZO films for application as transparent electrodes (TEs) in optoelectronic devices was evaluated, and the optimum laser power required for effective patterning was determined by analyzing the surface microstructures of the patterned films. Finally, to confirm the practical applicability of the SSedGZO films as TEs, electrochromic devices (ECDs) comprising the SSedGZO TEs were fabricated. The laser-patterned SSedGZO TEs functioned successfully in the fabricated ECDs, displaying reversible color changes through electrochromic switching.  相似文献   
972.
973.
Intervertebral disc (IVD) degeneration can cause chronic lower back pain (LBP), leading to disability. Despite significant advances in the treatment of discogenic LBP, the limitations of current treatments have sparked interest in biological approaches, including growth factor and stem cell injection, as new treatment options for patients with chronic LBP due to IVD degeneration (IVDD). Gene therapy represents exciting new possibilities for IVDD treatment, but treatment is still in its infancy. Literature searches were conducted using PubMed and Google Scholar to provide an overview of the principles and current state of gene therapy for IVDD. Gene transfer to degenerated disc cells in vitro and in animal models is reviewed. In addition, this review describes the use of gene silencing by RNA interference (RNAi) and gene editing by the clustered regularly interspaced short palindromic repeats (CRISPR) system, as well as the mammalian target of rapamycin (mTOR) signaling in vitro and in animal models. Significant technological advances in recent years have opened the door to a new generation of intradiscal gene therapy for the treatment of chronic discogenic LBP.  相似文献   
974.
Long-term design and planning of shale gas field development is challenging due to the complex development operations and a wide range of candidate locations. In this work, we focus on the multi-period shale gas field development problem, where the shale gas field has multiple formations and each well can be developed from one of several alternative pads. The decisions in this problem involve the design of the shale gas network and the planning of development operations. A mixed-integer linear programming (MILP) model is proposed to address this problem. Since the proposed model is a large-scale MILP, we propose a solution pool-based bilevel decomposition algorithm to solve it. Results on realistic instances demonstrate the value of the proposed model and the effectiveness of the proposed algorithm.  相似文献   
975.
Governing the fundamental reaction in lithium–oxygen batteries is vital to realizing their potentially high energy density. Here, novel oxygen reduction reaction (ORR) catalysts capable of mediating the lithium and oxygen reaction within a solution‐driven discharge, which promotes the solution‐phase formation of lithium peroxide (Li2O2), are reported, thus enhancing the discharge capacity. The new catalysts are derived from mimicking the biological redox mediation in the electron transport chain in Escherichia coli, where vitamin K2 mediates the oxidation of flavin mononucleotide and the reduction of cytochrome b in the cell membrane. The redox potential of vitamin K2 is demonstrated to coincide with the suitable ORR potential range of lithium–oxygen batteries in aprotic solvent, thereby enabling its successful functioning as a redox mediator (RM) triggering the solution‐based discharge. The use of vitamin K2 prevents the growth of film‐like Li2O2 even in an ether‐based electrolyte, which has been reported to induce surface‐driven discharge and early passivation of the electrode, thus boosting the discharge capacity by ≈30 times. The similarity of the redox mediation in the biological cell and lithium–oxygen “cell” inspires the exploration of redox active bio‐organic compounds for potential high‐performance RMs toward achieving high specific energies for lithium–oxygen batteries.  相似文献   
976.
977.
An experiment was conducted to examine effects of supplemental lysophospholipids (LPL) in dairy cows. Eight ruminally cannulated lactating Holstein cows were used in a replicated 4 × 4 Latin square design. Dietary treatments were (1) a dairy ration [CON; 55% forage and 45% concentrate on a dry matter (DM) basis], (2) a positive control diet supplemented with monensin (MON; 16 mg/kg in dietary DM; Elanco Animal Health, Greenfield, IN], (3) a control diet supplemented with low LPL (0.05% of dietary DM; Lipidol Ultra, Easy Bio Inc., Seoul, South Korea), and (4) a control diet supplemented with high LPL (0.075% of dietary DM). Experimental periods were 21 d with 14-d diet adaptation and 7-d sample collection. Daily intake and milk yield were measured and rumen contents were collected for fermentation characteristics and bacterial population. Spot urine and fecal samples (8 samples/cow per period) were collected to determine nutrient digestibility and dietary N utilization. All data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC; group and cow within group were random effects and treatments, time, and their interaction were fixed effects). Preplanned contrasts were made to determine effect of MON versus CON, effect of LPL versus MON, and linear effect of increasing LPL. In the current study, responses to MON generally agreed with effects of monensin observed in the literature (increased milk yield and feed efficiency but decreased milk fat content). Supplementation of LPL to the diet did not alter DM intake but linearly increased milk yield, resulting in increases in feed efficiency (milk yield/DM intake) and milk protein and fat yields. However, total-tract digestibility of DM and organic matter tended to be lower (60.9 vs. 62.2% and 61.8 vs. 63.1%, respectively) for LPL compared with CON. Linear increases in milk N secretion and decreases in urinary N excretion were observed with increasing LPL in the diet. A slight decrease in acetate proportion in the rumen for LPL was found. Relative to MON, very few bacteria in the rumen were affected with increasing LPL. In conclusion, LPL is a potential feed additive that can increase milk yield and components and dietary N utilization. However, more studies with large numbers of animals are needed to confirm the effect of LPL on production. Similar positive effects on production were observed between LPL and MON, but individual mechanisms were likely different according to ruminal fermentation characteristics. Further studies are needed to explore the mode of action of LPL in dairy cows.  相似文献   
978.
With the development of advanced and minimally invasive surgical techniques, and in view of the functional and cosmetic aspects, the need for rapid and accurate diagnosis during surgery is increasing. This study was conducted to develop a tissue diagnosis method using confocal microscopy after simple tissue staining that does not require freezing and slicing. At present, fluorescence staining with confocal microscopy is not generalized for real‐time diagnosis during surgery. In this paper, we propose a fluorescence staining method using Hoechst 33342 and Eosin that does not require tissue freezing and slicing. The proposed method can be used as part of a rapid tissue diagnosis method that is suitable for use in the operating room, although further research is required before it can be applied in clinical practice.  相似文献   
979.
980.
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