全文获取类型
收费全文 | 151862篇 |
免费 | 1888篇 |
国内免费 | 656篇 |
专业分类
电工技术 | 3115篇 |
综合类 | 187篇 |
化学工业 | 24072篇 |
金属工艺 | 5781篇 |
机械仪表 | 4943篇 |
建筑科学 | 4418篇 |
矿业工程 | 377篇 |
能源动力 | 3927篇 |
轻工业 | 17307篇 |
水利工程 | 1140篇 |
石油天然气 | 618篇 |
武器工业 | 5篇 |
无线电 | 20493篇 |
一般工业技术 | 28846篇 |
冶金工业 | 23754篇 |
原子能技术 | 2341篇 |
自动化技术 | 13082篇 |
出版年
2019年 | 834篇 |
2018年 | 1081篇 |
2017年 | 1131篇 |
2016年 | 1268篇 |
2015年 | 1063篇 |
2014年 | 1796篇 |
2013年 | 6575篇 |
2012年 | 3193篇 |
2011年 | 4608篇 |
2010年 | 3596篇 |
2009年 | 4151篇 |
2008年 | 4647篇 |
2007年 | 4913篇 |
2006年 | 4350篇 |
2005年 | 4108篇 |
2004年 | 4003篇 |
2003年 | 3899篇 |
2002年 | 3928篇 |
2001年 | 3980篇 |
2000年 | 3741篇 |
1999年 | 3691篇 |
1998年 | 6632篇 |
1997年 | 5227篇 |
1996年 | 4460篇 |
1995年 | 3709篇 |
1994年 | 3358篇 |
1993年 | 3184篇 |
1992年 | 2783篇 |
1991年 | 2690篇 |
1990年 | 2628篇 |
1989年 | 2614篇 |
1988年 | 2459篇 |
1987年 | 2166篇 |
1986年 | 2115篇 |
1985年 | 2556篇 |
1984年 | 2316篇 |
1983年 | 2195篇 |
1982年 | 2068篇 |
1981年 | 1991篇 |
1980年 | 1860篇 |
1979年 | 1874篇 |
1978年 | 1770篇 |
1977年 | 2085篇 |
1976年 | 2562篇 |
1975年 | 1583篇 |
1974年 | 1430篇 |
1973年 | 1453篇 |
1972年 | 1196篇 |
1971年 | 1115篇 |
1970年 | 948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
W Waespe 《Canadian Metallurgical Quarterly》1997,127(8):287-295
Benign paroxysmal vertigo and nystagmus are induced not only by the posterior but also by the horizontal semicircular canal. Benign positional nystagmus of the horizontal canal is more often observed than was previously thought. In 10 patients we analyzed the characteristics and the variability of nystagmus which accompanies positional vertigo of the horizontal canal. There are two forms of nystagmus: primary-geotropic, most often paroxysmal nystagmus (7 patients), and primary-apogeotropic, non-paroxysmal nystagmus (3 patients). Interestingly, in 2 patients with the primary-apogeotropic form the nystagmus converted during the examination into the primary-geotropic form. The reverse was not observed. We discuss the possible pathophysiological mechanisms which could be relevant for provoking manoeuvres. 相似文献
992.
993.
JM Rabey H Bass U Bonuccelli D Brooks P Klotz AD Korczyn P Kraus P Martinez-Martin P Morrish W Van Sauten B Van Hilten 《Canadian Metallurgical Quarterly》1997,20(4):322-337
The extensive use of the Unified Parkinson's Disease Rating Scale (UPDRS) has revealed low interrater reliability in some items and redundancy in others. In view of these shortcomings, we have structured a new scale that includes a zero-to three-point scale for each item in the evaluation of PD. The mental axis includes memory, thought disorders, and depression. Activities of daily living (ADL) includes eight items: speech, eating, feeding, dressing, hygiene, handwriting, walking, and turning in bed. The motor examination includes eight items: speech, tremor, rest and posture, rigidity, finger tapping, arising from chair, gait, and postural stability. Complications of therapy were also included: dyskinesias, dystonia, motor fluctuations, and freezing episodes, collected by history. In addition, a global scoring for motor fluctuations that should complement the Hoehn and Yahr Scale was incorporated. In this report, we present a statistical analysis of the ADL, motor evaluation, and complications of therapy sections. Concerning the interrater reliability mean, Kendall's W values were >0.9 for most of the items in the Short Parkinson's Evaluation Scale (SPES). Kendall's W <0.8 (motor evaluation) was found for two items of the SPES and nine items of the UPDRS. The mean interrater reliability for both scales across all seven centers (seven Kendall's W for seven centers) (Mann-Whitney test) showed no statistical differences between the scales. Spearman's correlations between items of both scales were significant. Factor analysis of the SPES and UPDRS data revealed a four-factor solution that explained approximately 60% of the data. All participating centers found the SPES easier to apply and quicker to complete, when compared with the UPDRS. The results obtained strongly favor the introduction of SPES for clinical practice. 相似文献
994.
The phase diagram and thermodynamic properties of the Hg–Tl binary system were modeled by means of the CALPHAD method, using experimental information as reported in the literature. A good agreement was observed between our calculated data and the existing experimental data. Also, an interesting result was established about the dependence of entropy and enthalpy of mixing functions on temperature, and at the same time, on practically ideal activity vs. concentration. The Gamma phase was described for the first time using the substitional RKMP model. 相似文献
995.
996.
997.
998.
The hydrides of the ternary alloys of CeNi5?xMx (M = Mn or Al and x = 0.5 and 0.75) have been prepared and investigated. The absorption plateau pressure of the system CeNi5—H is reduced 8- to 75-fold, by the replacement of Ni by Mn (or Al), without significantly impairing its hydrogen capacity. This substitution has great influence in reducing the hysteresis effect associated with the hydrogen absorption and desorption. The hysteresis and plateau-sloping factors are very low compared with that in Mischmetal-Ni5 hydride. The enthalpies and entropies of hydrogenation and dehydrogenation for CeNi5?xMx are computed and found to be in the range 20–25 kJ(mole H2)?1) and ~90–100 J(K mole H2)?1, respectively. The high effective entropies of the hydride (high configurational entropy of H in the lattice) are attributed to extensive hydrogen disorder in the interstitial sites of the CeNi5?xMx lattice. Desorption of the hydrogen in the two-phase region (α + β) for CeNi4.25Mn0.75-H follows first-order kinetics with an activation energy of ~33 ± 1 kJ(mole)?1. The favorable physiochemical properties of CeNi5?xMnx-H system make it very attractive for applications. 相似文献
999.
“To understand and protect our home planet, to explore the universe and search for life, and to inspire the next generation of explorers” is NASA's mission. The Systems Management Office at Johnson Space Center (JSC) is searching for methods to effectively manage the Center's resources to meet NASA's mission. D-Side is a group multi-criteria decision support system (GMDSS) developed to support facility decisions at JSC. D-Side uses a series of sequential and structured processes to plot facilities in a three-dimensional (3-D) graph on the basis of each facility's alignment with NASA's mission and goals, the extent to which other facilities are dependent on the facility, and the dollar value of capital investments that have been postponed at the facility relative to the facility's replacement value. A similarity factor rank orders facilities based on their Euclidean distance from Ideal and Nadir points. These similarity factors are then used to allocate capital improvement resources across facilities. We also present a parallel model that can be used to support decisions concerning allocation of human resources investments across workforce units. Finally, we present results from a pilot study where 12 experienced facility managers from NASA used D-Side and the organization's current approach to rank order and allocate funds for capital improvement across 20 facilities. Users evaluated D-Side favorably in terms of ease of use, the quality of the decision-making process, decision quality, and overall value-added. Their evaluations of D-Side were significantly more favorable than their evaluations of the current approach. 相似文献
1000.
Rosen James C.; Grubman James A.; Bevins Thomas; Frymoyer John W. 《Canadian Metallurgical Quarterly》1987,6(6):581
Studied Minnesota Multiphasic Personality Inventory (MMPI) profiles of 362 patients with acute and chronic low back pain (LBP) for replicable homogeneous subgroups using 3 cluster-analysis procedures. Two normal and 3 clinically elevated profile subgroups were identified. The 2 normal subgroups were characterized by relatively normal musculoskeletal condition and were least disabled but differed from each other in duration of pain, presence of physical abnormalities, and daily functioning. The most pathologic profile subgroup consisted largely of acute-pain patients whose musculoskeletal condition and daily functioning were similar to those of the normal subgroups. Patients in the 3 abnormal MMPI subgroups were exposed to more LBP physical-risk factors in the workplace. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献