全文获取类型
收费全文 | 77499篇 |
免费 | 8350篇 |
国内免费 | 4762篇 |
专业分类
电工技术 | 4912篇 |
技术理论 | 11篇 |
综合类 | 9908篇 |
化学工业 | 6568篇 |
金属工艺 | 2306篇 |
机械仪表 | 3548篇 |
建筑科学 | 15683篇 |
矿业工程 | 2961篇 |
能源动力 | 1678篇 |
轻工业 | 4838篇 |
水利工程 | 2510篇 |
石油天然气 | 2848篇 |
武器工业 | 606篇 |
无线电 | 6725篇 |
一般工业技术 | 8111篇 |
冶金工业 | 3587篇 |
原子能技术 | 806篇 |
自动化技术 | 13005篇 |
出版年
2024年 | 797篇 |
2023年 | 1248篇 |
2022年 | 2076篇 |
2021年 | 2346篇 |
2020年 | 2337篇 |
2019年 | 2083篇 |
2018年 | 1941篇 |
2017年 | 2267篇 |
2016年 | 2571篇 |
2015年 | 2698篇 |
2014年 | 4618篇 |
2013年 | 4369篇 |
2012年 | 5263篇 |
2011年 | 5599篇 |
2010年 | 4598篇 |
2009年 | 4777篇 |
2008年 | 4538篇 |
2007年 | 5334篇 |
2006年 | 4798篇 |
2005年 | 4104篇 |
2004年 | 3486篇 |
2003年 | 3068篇 |
2002年 | 2598篇 |
2001年 | 2209篇 |
2000年 | 1935篇 |
1999年 | 1573篇 |
1998年 | 1148篇 |
1997年 | 976篇 |
1996年 | 874篇 |
1995年 | 817篇 |
1994年 | 610篇 |
1993年 | 512篇 |
1992年 | 441篇 |
1991年 | 296篇 |
1990年 | 293篇 |
1989年 | 265篇 |
1988年 | 228篇 |
1987年 | 157篇 |
1986年 | 115篇 |
1985年 | 106篇 |
1984年 | 86篇 |
1983年 | 43篇 |
1982年 | 51篇 |
1981年 | 56篇 |
1980年 | 45篇 |
1979年 | 39篇 |
1978年 | 23篇 |
1977年 | 28篇 |
1976年 | 26篇 |
1975年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The condition of the surfaces is of crucial importance for the deuterium permeation through materials. In this work a study of the surface constants for the adsorption (σk1) and release (σk2) of deuterium under different surface conditions on the martensitic steel DIN 1.4914 (MANET) has been carried out. The growth of an oxide surface layer (Cr2O3) of about 25–30 nm in a MANET sample, heat treated in an oxidizing environment, compared to the bare MANET that have a ‘natural' oxide of about 5 nm has provoked a reduction of both the permeation rate and the recombination coefficient (about 3 orders of magnitude). In addition, the permeation governing process has changed from diffusion-limited to surface-limited. The measurements of the permeation rate of deuterium were performed by a gas-phase permeation technique over the temperature range 574–746 K and for deuterium driving pressures in the range from 3 to 105 Pa. 相似文献
22.
CIE TC8‐01 has adopted a new color appearance model: CIECAM021 replaces the CIECAM97s.2 The new model consists of a number of refinements and simplifications of the CIECAM97s color appearance model. This article describes further tests to the robustness of the forward and reverse modes. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 99–106, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20087 相似文献
23.
24.
人体内微量元素含量平衡与否与人体健康状态有着密切关系已为大量实践所证实。人体血液中微量元素的正常值测定是研究人体健康与微量元素关系的一项基础性工作,本文提供了天津市正常人全血及血清中几种微量元素含量的数据。 相似文献
25.
26.
Discusses retouching of the Kallikak family photographs in H. H. Goddard's (1912) study of mental retardation and heredity, with reference to analyses by R. E. Fancher (see record 1987-31600-001) and S. J. Gould (1981), and concurs with Fancher that the retouching was probably not done for deceitful purposes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
Examined the 10 most cited articles published in the Psychological Bulletin over the past 4 decades. Seven of the 10 articles were methodologically oriented. A survey of the authors revealed that highly cited articles have an important message that goes beyond momentary fads, are broad in topic and intended audience, accessible, and well written. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
D. T. Cambell and D. W. Fiske (1959) made the now-obvious statement that measures of the same variable made by different methods should agree (converge) and certainly should agree better than measures of different variables made by those several methods. Almost everyone accepted that statement, yet the multitrait–multimethod matrices published today show little or no improvement over the published examples cited in 1959. The article raised the conceptual problem of how a variable and its measurement should be linked and the methodological problem of clarifying the nature of methods and their effects. Given these unresolved problems, it is perhaps not surprising that the question of the appropriate statistical analysis of these matrices has also no consensual answer. Perhaps methods and traits or contents are so thoroughly intertwined that their interaction cannot be adequately analyzed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
The nonlinear Boussinesq equation is used to understand water table fluctuations in various ditch drainage problems. An approximate solution of this equation with a random initial condition and deterministic boundary conditions, recharge rate and aquifer parameters has been developed to predict a transient water table in a ditch-drainage system. The effects of uncertainty in the initial condition on the water table are illustrated with the help of a synthetic example. These results would find applications in ditch-drainage design.Notation
A
/ tanh t
-
a
lower value of the random variable representing the initial water table height at the mid point
-
a+b
Upper value of the random variable representing the initial water table height at the midpoint
-
B
tanh t
-
C
4/
-
h
variable water table height
- h
mean of the variable water table height
-
h
m
variable water table height at the mid point
- h
m
mean of the variable water table height at the mid point
-
K
hydraulic conductivity
-
L
half spacing between the ditches
-
m
0
initial water table height at the mid point
-
N
Uniform rate of recharge
-
S
specific yield
-
t
time of observation
-
x
distance measured from the ditch boundary
-
(4/SL)(NK)1/2
-
(L/4)(N/K)1/2
-
dummy integral variable 相似文献
30.
本文研制了一台测量电子束和β射线吸收剂量的外推电离室,其空腔室壁材料可拆换并分别与空气、组织和硅等效,收集电极名义直径为1.5、3、10和30mm,空气空腔可变范围为0.2~15mm。该外推电离室具有在空腔内部测温,自动改变窗口上方材料厚度及采用微型计算机控制等特点。适用于测10 MeV能量以下,剂量率为10~5~10~(-3)Gy/h的电子或β射线吸收剂量。整个外推电离室自动测剂量系统在测~(204)TLβ放射源表面剂量率的不确定度为2.3%。测1.5 MeV电子束在硅和哈密瓜深部剂量率时,不确定度分别为4.0%和2.8%。 相似文献