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   3001篇
  免费   105篇
  国内免费   18篇
电工技术   55篇
综合类   16篇
化学工业   657篇
金属工艺   46篇
机械仪表   66篇
建筑科学   45篇
矿业工程   3篇
能源动力   139篇
轻工业   279篇
水利工程   18篇
石油天然气   14篇
无线电   317篇
一般工业技术   599篇
冶金工业   465篇
原子能技术   25篇
自动化技术   380篇
  2023年   29篇
  2022年   57篇
  2021年   114篇
  2020年   74篇
  2019年   77篇
  2018年   94篇
  2017年   81篇
  2016年   98篇
  2015年   52篇
  2014年   94篇
  2013年   166篇
  2012年   126篇
  2011年   153篇
  2010年   117篇
  2009年   100篇
  2008年   117篇
  2007年   113篇
  2006年   95篇
  2005年   89篇
  2004年   59篇
  2003年   56篇
  2002年   48篇
  2001年   28篇
  2000年   42篇
  1999年   39篇
  1998年   162篇
  1997年   104篇
  1996年   89篇
  1995年   57篇
  1994年   63篇
  1993年   54篇
  1992年   38篇
  1991年   33篇
  1990年   23篇
  1989年   25篇
  1988年   25篇
  1987年   16篇
  1986年   21篇
  1985年   26篇
  1984年   32篇
  1983年   14篇
  1982年   20篇
  1981年   19篇
  1980年   19篇
  1978年   18篇
  1977年   17篇
  1976年   31篇
  1975年   15篇
  1974年   20篇
  1972年   13篇
排序方式: 共有3124条查询结果,搜索用时 31 毫秒
21.
Urinary protein and calcium excretion were assessed in 77 patients with the hepatic glycogen storage diseases (GSD): 30 with GSD-I (median age 12.4 years, range 3.2-32.9 years), 25 with GSD-III (median age 10.5 years, range 4.2-31.3 years) and 22 with GSD-IX (median age 11.8 years, range 1.2-35.4 years). Inulin (Cinulin) and para-aminohippuric acid (CPAH) clearances were also measured in 33 of these patients. Those with GSD-I had significantly greater albumin (F = 15.07, P < 0.001), retinol-binding protein (RBP) (F = 14.66, P < 0.001), N-acetyl-beta-D-glucosaminidase (NAG) (F = 9.41, P < 0.001) and calcium (F = 7.41, P = 0.001) excretion than those with GSD-III and GSD-IX. GSD-I patients (n = 18) also had significantly higher Cinulin (F = 5.57, P = 0.009), but CPAH did not differ (F = 0.77, NS). Renal function was normal in GSD-III and GSD-IX patients. In GSD-I, Cinulin (r = -0.51, P = 0.03) and NAG excretion (r = -0.40, P = 0.03) were inversely correlated with age, whereas albumin excretion was positively correlated with age (r = +0.41, P = 0.03). RBP and calcium excretion were generally high throughout all age groups. Hyperfiltration in GSD-I is associated with renal tubular proteinuria that occurs before the onset of significant albuminuria. Deficiency of glucose-6-phosphatase within the proximal renal tubule may primarily cause tubular dysfunction, glomerular hyperfiltration being a secondary phenomenon.  相似文献   
22.
We address the issue of tracking moving objects in an environment covered by multiple uncalibrated cameras with overlapping fields of view, typical of most surveillance setups. In such a scenario, it is essential to establish correspondence between tracks of the same object, seen in different cameras, to recover complete information about the object. We call this the problem of consistent labeling of objects when seen in multiple cameras. We employ a novel approach of finding the limits of field of view (FOV) of each camera as visible in the other cameras. We show that, if the FOV lines are known, it is possible to disambiguate between multiple possibilities for correspondence. We present a method to automatically recover these lines by observing motion in the environment, Furthermore, once these lines are initialized, the homography between the views can also be recovered. We present results on indoor and outdoor sequences containing persons and vehicles.  相似文献   
23.
Precipitation of nickel ammonium sulphate achieved by mixing solutions of nickel sulphate and ammonium sulphate in a 5 1 MSMPR crystallizer is used to investigate both crystallization and agglomeration kinetics from the steady-state crystal size distribution. An iterative non-linear parameter estimation procedure is used to deduce the kinetic rate parameters in the solution of the agglomeration model suggested by Liao and Hulburt from the data-set obtained by size analysis of the product crystals. The results obtained are correlated in terms of conventional power law kinetic expressions.  相似文献   
24.
It is conjectured that anionic-cationic surfactant combination can be regarded as equivalent to a double chain surfactant and using molecular packing considerations it is shown that vesicles, viscoelastic solutions and liquid crystals can be designed by the proper choice of chain lengths of the pair. Using these concepts new systems are designed, from mixtures of cetyltrimethyl ammonium bromide and sodium alkyl sulfonates, to produce both viscoelastic gels and vesicles.  相似文献   
25.
Geometry-Dependent R-Curve for Quasi-Brittle Materials   总被引:4,自引:0,他引:4  
Fracture of quasi-brittle materials such as ceramics and cement-based materials can be described by an R -curve, defined as fracture resistance. The R -curve can be constructed as the envelope of the strain energy release rates ( G ). In this study, R -curve is defined as an envelope of G -curves obtained by varying the dimensions of identical specimens, while keeping the geometry and the initial flaw size constant. By approximating the G -curve with a second-order function of the crack length, a simple formulation of the R -curve is derived by solving a differential equation. Three parameters are needed for the proposed R -curve. These parameters can be obtained by testing a notched-beam specimen and using linear elastic fracture mechanics. The proposed R -curve simulates well the geometry dependency as well as other characteristics of the fracture response of quasi-brittle materials.  相似文献   
26.
A routing protocol chooses one of the several paths (routes) from a source node to a destination node in the computer network, to send a packet of information. In this paper, we propose a new routing protocol, which we call st-routing protocol, based on st-numbering of a graph. The protocol fits well in noisy environments where robustness of routing using alternative paths is a major issue. The proposed routing protocol provides a systematic way to retry alternative paths without generating any duplicate packets. The protocol works for only those networks that can be represented by biconnected graphs.  相似文献   
27.
Litchi (Litchi chinensis Sonn.) fruits are very susceptible to pericarp browning which adversely affects consumer acceptability even though the aril portion remains in excellent condition. Litchi arils (litchis) were treated with a solution containing 0–2% (w/v) calcium lactate (CL), 0–0.02% (w/v) 4‐hexyl resorcinol (4‐HR) and 1% potassium sorbate. The pH of solution was adjusted to 4.0 with citric acid. Treated litchis were packed in polystyrene trays, over‐wrapped with polypropylene film, vacuum‐packed (0, 47409.3, 94831.9 Pa) and stored at 4 ± 2 °C. Drip losses, pH, total soluble solids (TSS), sensory attributes and microbiological quality of stored samples were estimated. A four‐factor, three‐level experimental design (D6 Hokes design) with 19 experiments was chosen. Mathematical models were developed to analyse and predict the effect of CL, 4‐HR, in‐package vacuum and storage time on the responses. TSS, pH and sensory scores decreased significantly (P 0.01), whereas drip losses and microbial count increased significantly (P 0.01) with time. Drip loss was significantly (P 0.1) reduced by addition of CL. 4‐HR prevented browning and changes in colour score during storage were significantly less. Vacuum in packages exerted significant (P 0.01) effect over pH, TSS, sensory and microbiological qualities of minimally processed litchis.  相似文献   
28.
Precast bridges are often constructed as single span for dead load, but continuous for live load. A diaphragm connection is provided for negative moment continuity. However, the connection may also be subjected to positive moments due to time-dependent effects. Because these moments may be large enough to damage the diaphragm or even the girders, a positive moment connection is often provided. This paper reports on a study to determine the types of positive moment connections used across the country and to identify potential problems with these types of connections. A questionnaire survey was conducted to assess the state of practice for precast prestressed concrete bridges made continuous. The survey provides valuable information on this type of bridge and updates a previous survey on this subject.  相似文献   
29.
30.
Polypropylene mesh, the routinely used material for mesh laparostomies is expensive. A economical and easily available substitute-nylon net was compared with polypropylene mesh with regard to efficacy and wound complications in a retrospective study. 51 patients, 25 in the polypropylene mesh group and 26 in the nylon net group were studied. The groups were matched with respect to age, sex, indication for surgery and mortality. The mean hospital stay (65 vs 54 days), fate of the wound, incidence of mesh extrusion (26% vs 20%), bowel perforation (1 vs none) and incisional hernia formation (21% vs 20%) in those with polypropylene mesh and nylon net respectively was similar. In conclusion, nylon net is an effective and inexpensive indigenous substitute for polypropylene mesh for mesh laparostomies.  相似文献   
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