全文获取类型
收费全文 | 5108篇 |
免费 | 69篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 19篇 |
综合类 | 4篇 |
化学工业 | 387篇 |
金属工艺 | 33篇 |
机械仪表 | 83篇 |
建筑科学 | 124篇 |
矿业工程 | 3篇 |
能源动力 | 67篇 |
轻工业 | 234篇 |
水利工程 | 27篇 |
石油天然气 | 9篇 |
无线电 | 307篇 |
一般工业技术 | 413篇 |
冶金工业 | 3135篇 |
原子能技术 | 29篇 |
自动化技术 | 309篇 |
出版年
2021年 | 23篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 27篇 |
2016年 | 41篇 |
2015年 | 29篇 |
2014年 | 36篇 |
2013年 | 110篇 |
2012年 | 66篇 |
2011年 | 91篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 97篇 |
2007年 | 89篇 |
2006年 | 77篇 |
2005年 | 78篇 |
2004年 | 61篇 |
2003年 | 67篇 |
2002年 | 75篇 |
2001年 | 62篇 |
2000年 | 64篇 |
1999年 | 145篇 |
1998年 | 987篇 |
1997年 | 503篇 |
1996年 | 366篇 |
1995年 | 196篇 |
1994年 | 191篇 |
1993年 | 211篇 |
1992年 | 54篇 |
1991年 | 58篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 87篇 |
1987年 | 72篇 |
1986年 | 49篇 |
1985年 | 59篇 |
1984年 | 42篇 |
1983年 | 34篇 |
1982年 | 44篇 |
1981年 | 59篇 |
1980年 | 51篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 79篇 |
1976年 | 179篇 |
1975年 | 32篇 |
1974年 | 29篇 |
1973年 | 17篇 |
1971年 | 19篇 |
1970年 | 20篇 |
排序方式: 共有5183条查询结果,搜索用时 687 毫秒
31.
32.
The present investigation provide evidences from a non-human primate model that naturally occurring menopause predicts a prominent signature of age-related cognitive decline. Young and aged rhesus monkeys were tested on a delayed response (DR) task known to the sensitive to aging, and reproductive status was evaluated according to menstrual cyclicity and urinary hormone profiles. Peri-/postmenopausal monkeys exhibited significant DR impairments relative to either age-matched premenopausal females, or young control subjects. In addition, markers of endocrine decline in the aged animals were selectively correlated with behavioral performance measures that distinguished premenopausal and peri-/postmenopausal monkeys. These results document that menopause is coupled to cognitive decline in the monkey, and they establish a valuable primate model for defining the effects of endocrine aging on brain and behavioral function. 相似文献
33.
34.
Recent research suggests that implementing information systems presents considerable difficulties and that many implementations are total or partial failures. This paper argues that what both practitioners and students require are richer and more acceptable models of information systems implementation. Accordingly, case study data concerning the introduction of manufacturing resource planning (MRP II) are used to illustrate five patterns of behaviour (rites) which capture important social actions; and four components of changing psychological orientation. It is argued that appreciation of the rites and psychological developments identified here will support effective change programmes. Guidelines based on our model are provided for practitioners. 相似文献
35.
Composite metacarpophalangeal joint reconstruction using the toe proximal phalanx and the metacarpal head, with a capsular repair, is an option during free toe transfer procedures for absent fingers. Eleven composite metacarpophalangeal finger joint reconstructions were performed in four patients concurrent with combined second and third toe-to-hand transfer. The average follow-up period was 5 years. Postoperative assessment included range of motion, stability, radiographic changes, and pain. The average range of motion was 52 degrees, average ulnar stress deviation was 14 degrees. No patients complained of pain. Composite metacarpophalangeal joint reconstruction should be considered in free toe-to-hand procedures when metacarpal head articular cartilage is preserved. 相似文献
36.
CM Tsai SH Hsiao CM Frey KT Chang RP Perng AF Gazdar BS Kramer 《Canadian Metallurgical Quarterly》1993,53(5):1079-1084
Both cisplatin (CDDP) and leucovorin (LV) have been shown to enhance cytotoxicity of 5-fluorouracil (FUra) against murine and human neoplasms by increasing intracellular reduced folate concentrations. We were interested in their use in a combination to inhibit non-small cell lung cancer (NSCLC) cell growth and therefore conducted an in vitro study to investigate the cytotoxic activities of combinations of CDDP plus FUra, with and without LV (20 microM), against seven NSCLC cell lines. A tetrazolium assay with application of the classical isobole method was used to test drug combinations. We found that LV enhanced FUra but not CDDP cytotoxicity and that the degree of enhancement was negatively correlated with the effect of FUra. There was an overall additive combination effect of CDDP plus FUra, although there may be synergy at higher effect levels. There was synergy to a combination of CDDP, FUra, and LV, presumably primarily related to the synergistic effects of adding LV to FUra. In summary, LV and CDDP enhanced FUra cytotoxicity in a complementary fashion and there was clear synergy of a combination of CDDP, FUra, and LV against a panel of NSCLC cell lines. Our in vitro results provide a rationale for controlled clinical studies of this three-drug regimen in patients with NSCLC. 相似文献
37.
Lewinsohn Peter M.; Hops Hyman; Roberts Robert E.; Seeley John R.; Andrews Judy A. 《Canadian Metallurgical Quarterly》1993,102(4):517
Reports an error in the original article by P. M. Lewinsohn et al ( Journal of Abnormal Psychology, 1993[Feb], Vol 102[1], 133–244). On page 140, in the Total Incidence columns in Table 4, the data for the Attention Deficit row should be switched with that for the Conduct row. (The following abstract of this article originally appeared in record 1993-25780-001.) Data were collected on the point and lifetime prevalences, 1-yr incidence, and comorbidity of depression with other Diagnostic and Statistical Manual of Mental Disorders-III-Revised (DSM-III-R) disorders in a randomly selected sample (n?=?1,710) of high school students at point of entry and at 1-yr follow-up (n?=?1,508). The Schedule for Affective Disorders and Schizophrenia for School-Age Children was used to collect diagnostic information; 9.6% met criteria for a current disorder, more than 33% had experienced a disorder over their lifetimes, and 31.7% of the latter had experienced a 2nd disorder. High relapse rates were found for all disorders, especially for unipolar depression (18.4%) and substance use (15.0%). Female Ss had significantly higher rates at all age levels for unipolar depression, anxiety disorders, eating disorders, and adjustment disorders; male Ss had higher rates of disruptive behavior disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
38.
39.
Empirical research pertaining to cardiopulmonary resuscitation (CPR), clinician behaviors related to do-not-resuscitate (DNR) orders and substituted judgment suggests potential contributions to medical ethics. Research quantifying the likelihood of surviving CPR points to the need for further philosophical analysis of the limitations of the patient autonomy in decision making, the nature and definition of medical futility, and the relationship between futility and professional standards. Research on DNR orders has identified barriers to the goal of patient involvement in these life and death discussions. The initial data on surrogate decision making also points to the need for a reexamination of the moral basis for substituted judgment, the moral authority of proxy decision making and the second-order status of the best interests standard. These examples of empirical research suggest that an interplay between empirical research, ethical analysis and policy development may represent a new form of interdisciplinary scholarship to improve clinical medicine. 相似文献
40.
OBJECTIVE: To describe a simple injection apparatus and method for performing intracytoplasmic sperm injection in a clinical IVF program. DESIGN: A prospective clinical trial of intracytoplasmic sperm injection. SETTING: A private office-based fertility program. PATIENTS: Five couples undergoing IVF-ET with intracytoplasmic sperm injection as a treatment for male factor infertility. INTERVENTIONS: Intracytoplasmic sperm injection was performed at room temperature (23.5 to 24.5 degrees C) in a simple zwitterion-buffered medium. MAIN OUTCOME MEASURES: Fertilization rates, cleavage rates, clinical pregnancy rates, implantation rates. RESULTS: Intracytoplasmic sperm injection was performed on 44 fresh oocytes from five patients. Twenty-three oocytes fertilized (52.3%) and 22 zygotes cleaved (95.7%). Three of five patients became pregnant (60%), resulting in the live birth of one normal male infant, one continuing singleton pregnancy, and one continuing twin gestation (46XX, 46XY). The implantation rate was 23.5%. CONCLUSION: Intracytoplasmic sperm injection can be performed successfully in a simple medium at room temperature using commercially available microtools. 相似文献