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   528篇
  免费   14篇
  国内免费   1篇
电工技术   5篇
综合类   1篇
化学工业   76篇
金属工艺   11篇
机械仪表   4篇
建筑科学   9篇
能源动力   3篇
轻工业   50篇
水利工程   1篇
石油天然气   1篇
无线电   9篇
一般工业技术   47篇
冶金工业   256篇
原子能技术   4篇
自动化技术   66篇
  2022年   5篇
  2018年   5篇
  2017年   7篇
  2014年   4篇
  2013年   24篇
  2012年   7篇
  2011年   11篇
  2010年   12篇
  2009年   14篇
  2008年   8篇
  2007年   11篇
  2006年   10篇
  2005年   13篇
  2004年   8篇
  2003年   15篇
  2002年   12篇
  2001年   6篇
  2000年   5篇
  1999年   19篇
  1998年   80篇
  1997年   47篇
  1996年   23篇
  1995年   22篇
  1994年   22篇
  1993年   17篇
  1992年   4篇
  1991年   4篇
  1990年   11篇
  1989年   10篇
  1988年   4篇
  1987年   4篇
  1986年   8篇
  1985年   5篇
  1984年   3篇
  1983年   3篇
  1982年   4篇
  1981年   6篇
  1980年   5篇
  1979年   3篇
  1978年   2篇
  1977年   11篇
  1976年   24篇
  1975年   4篇
  1972年   2篇
  1970年   2篇
  1963年   2篇
  1957年   2篇
  1942年   1篇
  1940年   1篇
  1930年   1篇
排序方式: 共有543条查询结果,搜索用时 15 毫秒
91.
The present study examined the role of maternal gatekeeping behavior in relation to fathers' relative involvement and competence in child care in 97 families with infant children. Parents' beliefs about fathers' roles were assessed prior to their infant's birth. Parents' perceptions of maternal gatekeeping behavior (encouragement and criticism) and coparenting relationship quality were assessed at 3.5 months postpartum. The authors assessed fathers' relative involvement and competence in child care using a combination of parent report and observational measures. Results suggest that even after accounting for parents' beliefs about the paternal role and the overall quality of the coparenting relationship, greater maternal encouragement was associated with higher parent-reported relative father involvement. Moreover, maternal encouragement mediated the association between coparenting quality and reported relative father involvement. With respect to fathers' observed behavior, fathers' beliefs and parents' perceptions of coparenting relationship quality were relevant only when mothers engaged in low levels of criticism and high levels of encouragement, respectively. These findings are consistent with the notion that mothers may shape father involvement through their roles as "gatekeepers." (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
92.
On the basis of results of studies using high doses of estrogens, exposure to estrogen during fetal life is known to inhibit prostate development. However, it is recognized in endocrinology that low concentrations of a hormone can stimulate a tissue, while high concentrations can have the opposite effect. We report here that a 50% increase in free-serum estradiol in male mouse fetuses (released by a maternal Silastic estradiol implant) induced a 40% increase in the number of developing prostatic glands during fetal life; subsequently, in adulthood, the number of prostatic androgen receptors per cell was permanently increased by 2-fold, and the prostate was enlarged by 30% (due to hyperplasia) relative to untreated males. However, as the free serum estradiol concentration in male fetuses was increased from 2- to 8-fold, adult prostate weight decreased relative to males exposed to the 50% increase in estradiol. As a model for fetal exposure to man-made estrogens, pregnant mice were fed diethylstilbestrol (DES) from gestation days 11 to 17. Relative to controls, DES doses of 0.02, 0.2, and 2.0 ng per g of body weight per day increased adult prostate weight, whereas a 200-ng-per-g dose decreased adult prostate weight in male offspring. Our findings suggest that a small increase in estrogen may modulate the action of androgen in regulating prostate differentiation, resulting in a permanent increase in prostatic androgen receptors and prostate size. For both estradiol and DES, prostate weight first increased then decreased with dose, resulting in an inverted-U dose-response relationship.  相似文献   
93.
Twenty of 67 children registered on the International Registry of Childhood Adrenocortical Tumors between May 1988 and December 1994 had small adrenocortical tumors (defined for this study as measuring < or = 200 cm3 and/or weighing < or = 100 g). We reviewed the records of these 20 patients to characterize the clinical and pathologic findings and outcomes of children with small adrenocortical tumors. Median patient age was 2 years (range, 4 months to 5 years). There was only one boy. All had clinical signs of virilization, and seven had signs or symptoms of Cushing syndrome. A median 5.5 months (range, 1-40 months) had elapsed between the first signs of endocrine dysfunction and diagnosis. All tumors were surgically resected. Tumor volume was 3.3-195 cm3 (median, -8.7 cm3), and weight was 3.7-100 g (median, 36 gm Tumor samples were histologically reviewed in 18 cases. Eight were adenomas, and 10 were carcinomas (6 low grade and 4 high grade). Pathology records described tumor with diagnostic features of adrenocortical carcinoma in two patients. One patient received mitotane for 8 months after surgery. Only one patient had recurrent disease, which was detected 6 months after diagnosis and proved rapidly fatal. Another has been lost to follow-up. The remaining 18 patients are alive with no evidence of disease at a median 2.3 years (range, 6 months to 6.1 years) after diagnosis. Our data suggest that children with small adrenocortical tumors have an excellent prognosis with surgery as the sole therapy, regardless of tumor histiotype.  相似文献   
94.
This study describes the design, methodologic features, and baseline characteristics of an open-label randomized trial to determine whether aggressive lipid-lowering therapy with atorvastatin is an alternative to angioplasty or other catheter-based revascularization procedures in patients with significant coronary artery disease. Three-hundred forty-one patients with low-density lipoprotein (LDL) cholesterol > or = 115 mg/dl and > or = 1 defined narrowing of a major coronary artery were randomized to atorvastatin or the indicated catheter-based revascularization and conventional care (including lipid-lowering therapy if prescribed). Ischemic events are tracked for 18 months. The primary efficacy parameter is the incidence of an ischemic event, defined as 1 of the following: cardiovascular death, cardiac arrest, nonfatal myocardial infarction, the need for coronary bypass grafting or angioplasty, cerebrovascular accident, and worsening angina verified by objective evidence requiring hospitalization (including unstable angina).  相似文献   
95.
Although atrophie blanche is classified as a vasculitis, its presentation and management differ from the classical vasculitis. We present a patient with idiopathic atrophie blanche and discuss its management.  相似文献   
96.
An abnormal hemodynamic response to stressful stimuli has been proposed as a mechanism involved in the higher prevalence of hypertension in blacks. Given the important role of nitric oxide (NO) in the regulation of cardiovascular homeostasis, we investigated the possibility of racial differences in vascular NO activity during mental stress. To test this hypothesis, we compared the forearm blood flow (FBF) response to mental stress in 14 white and 12 black healthy subjects during intra-arterial infusion of either saline or NO synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 4 micromol/min). We also examined vascular responses of the two groups to intra-arterial infusion of sodium nitroprusside (0.8 to 3.2 microg/min), an exogenous NO donor. During saline infusion, the increase in FBF from baseline induced by mental stress was significantly higher in whites than in blacks (109+/-20% versus 58+/-8%; P=0.03). L-NMMA significantly reduced stress-induced increase in FBF in whites (from 109+/-20% to 54+/-11%; P=0.004) but not in blacks (from 58+/-8% to 42+/-10%; P=0.24); thus, the vasodilator effect of stress testing during L-NMMA was similar in whites and blacks (54+/-11% versus 42+/-10%; P=0.44). The vasodilator response to sodium nitroprusside was also lower in blacks than in whites (maximum flow, 6.9+/-2 versus 11.6+/-3.5 mL x min(-1) x dL(-1); P=0.001) and was not significantly modified by L-NMMA in either group. Our findings indicate that blacks have a reduced NO-dependent vasodilator activity during mental stress. This difference seems related to reduced sensitivity of smooth muscle to the vasodilator effect of NO and may play some role in the increased prevalence of hypertension and its complications in blacks.  相似文献   
97.
BACKGROUND: To compare the efficacy and safety of tacrolimus and cyclosporine in heart transplantation, this single-center, prospective, randomized, open-label clinical trial was undertaken. METHODS: Seventy-three adult patients were randomly assigned at the time of transplantation to receive either tacrolimus (n=43) or cyclosporine (n=30) as the primary immunosuppressant. Ten of the 43 patients in the tacrolimus group received the drug intravenously in the perioperative period; all other patients received only oral tacrolimus. RESULTS: With a mean follow-up of 27 months, patient survival rates (tacrolimus 83%, cyclosporine 81%) were similar. Fewer patients experienced acute rejection in the tacrolimus group (79%) than in the cyclosporine group (100%), but the difference was not statistically significant. The number of infections and dialysis and insulin requirements were similar for the 2 treatment groups, but the proportion of patients requiring multidrug antihypertensive regimens was lower in the tacrolimus group (12.5% vs 50.0% at month 6; p=.025). The interpatient variance in pharmacokinetic parameters in a subset of 10 patients was much higher after the first oral dose of tacrolimus than at steady-state (eg, first-dose time at which maximal concentration is reached (t(max)): 3.5+/-2.5h, steady-state t(max): 2.0+/-0.7h), and patients treated with intravenous tacrolimus (n=13) rather than oral tacrolimus (n=30) reached target concentrations faster and with less interpatient variability (eg, at day 0: 9.72+/-10.9 ng/mL intravenously vs 3.31+/-8.1 orally). CONCLUSIONS: Tacrolimus was associated with similar efficacy and safety profiles compared with cyclosporine. The higher interpatient variance in absorption associated with oral tacrolimus during the first few days after transplantation would suggest that intravenous tacrolimus should be used during the perioperative period.  相似文献   
98.
The study aimed to evaluate the perception of discrimination in the Czech national HIV policy among gay men. The anonymous questionnaires were published in the gay journal and 191 respondents filled them and returned back. Their assessment of discrimination in the HIV policy and other life activities were ranked in 5-points scale. Assumed discrimination in the HIV policy was found to be one of the lowest one. Forty-one percent of men who answered did not find any discrimination in the HIV policy at all, eleven percent of them perceived it at the highest level. The personal perception of HIV discrimination was related to the fear of discrimination in the health facilities and to the general evaluation of political change for gay life. HIV policy is generally viewed as tolerant and without discriminative approach toward vulnerable minorities. The number of negative evaluations can play important role in the obstacles of preventive programs.  相似文献   
99.
BACKGROUND: Bolus thrombolytic therapy is a simplified means of administering thrombolysis that facilitates rapid time to treatment. TNK-tissue plasminogen activator (TNK-tPA) is a highly fibrin-specific single-bolus thrombolytic agent. METHODS AND RESULTS: In TIMI 10B, 886 patients with acute ST-elevation myocardial infarction presenting within 12 hours were randomized to receive either a single bolus of 30 or 50 mg TNK-tPA or front-loaded tPA and underwent immediate coronary angiography. The 50-mg dose was discontinued early because of increased intracranial hemorrhage and was replaced by a 40-mg dose, and heparin doses were decreased. TNK-tPA 40 mg and tPA produced similar rates of TIMI grade 3 flow at 90 minutes (62.8% versus 62.7%, respectively, P=NS); the rate for the 30-mg dose was significantly lower (54.3%, P=0.035) and was 65. 8% for the 50-mg dose (P=NS). A prespecified analysis of weight-based TNK-tPA dosing using median TIMI frame count demonstrated a dose response (P=0.001). Similar dose responses were observed for serious bleeding and intracranial hemorrhage, but significantly lower rates were observed for both TNK-tPA and tPA after the heparin doses were lowered and titration of the heparin was started at 6 hours. CONCLUSIONS: TNK-tPA, given as a single 40-mg bolus, achieved rates of TIMI grade 3 flow similar to those of the 90-minute bolus and infusion of tPA. Weight-adjusting TNK-tPA appears to be important in achieving optimal reperfusion; reduced heparin dosing appears to improve safety for both agents. Together with the safety results from the parallel Assessment of the Safety of a New Thrombolytic: TNK-tPA (ASSENT I) trial, an appropriate dose of this single-bolus thrombolytic agent has been identified for phase III testing.  相似文献   
100.
Two chemicals previously shown to have estrogenic activity, bisphenol A and octylphenol, were examined for their effects on accessory reproductive organs and daily sperm production in male offspring of mice fed these chemicals during pregnancy. These chemicals are used in the manufacture of plastics and other products, and have been detected in food and water consumed by animals and people. From gestation day 11-17 female mice were fed an average concentration (dissolved in oil) of bisphenol A or octylphenol of 2 ng/g body weight (2 ppb) and 20 ng/g (20 ppb). The 2 ppb dose of bisphenol A is lower than the amount reported to be swallowed during the first hour after application of a plastic dental sealant (up to 931 micrograms; 13.3 ppb in a 70 kg adult). We found that the 2 ng/g dose of bisphenol A permanently increased the size of the preputial glands, but reduced the size of the epididymides; these organs develop from different embryonic tissues. At 20 ng/g, bisphenol A significantly decreased efficiency of sperm production (daily sperm production per g testis) by 20% relative to control males. The only significant effect of octylphenol was a reduction in daily sperm production and efficiency of sperm production at the 2 ng/g dose. A new approach to studying physiologically relevant doses of environmental endocrine disruptors is discussed, particularly with regard to the development of the reproductive organs, the brain, and behavior.  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