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   4018篇
  免费   20篇
  国内免费   12篇
电工技术   12篇
综合类   16篇
化学工业   40篇
金属工艺   10篇
机械仪表   19篇
建筑科学   25篇
矿业工程   13篇
能源动力   6篇
轻工业   63篇
水利工程   5篇
石油天然气   6篇
武器工业   1篇
无线电   26篇
一般工业技术   23篇
冶金工业   3729篇
原子能技术   10篇
自动化技术   46篇
  2023年   3篇
  2022年   10篇
  2021年   17篇
  2020年   9篇
  2019年   11篇
  2018年   5篇
  2017年   2篇
  2016年   7篇
  2015年   10篇
  2014年   14篇
  2013年   30篇
  2012年   15篇
  2011年   20篇
  2010年   19篇
  2009年   16篇
  2008年   17篇
  2007年   14篇
  2006年   15篇
  2005年   27篇
  2004年   13篇
  2003年   10篇
  2002年   12篇
  2001年   7篇
  2000年   3篇
  1999年   113篇
  1998年   1225篇
  1997年   709篇
  1996年   412篇
  1995年   250篇
  1994年   194篇
  1993年   212篇
  1992年   38篇
  1991年   24篇
  1990年   43篇
  1989年   36篇
  1988年   47篇
  1987年   37篇
  1986年   36篇
  1985年   37篇
  1983年   4篇
  1982年   15篇
  1981年   20篇
  1980年   26篇
  1979年   2篇
  1978年   12篇
  1977年   82篇
  1976年   148篇
  1975年   11篇
  1973年   2篇
  1955年   3篇
排序方式: 共有4050条查询结果,搜索用时 0 毫秒
91.
The substance-use, positive health practices, diet and eating habits, driving behaviours and preventive health care practices of 113 nurses living in the southeast of England were assessed by means of a postal questionnaire. Females were generally more compliant than males with most of the behaviours assessed. Females reported taking greater risks with driving behaviours by an occasional tendency to "drink and drive". Many males reported both a lack of knowledge of how to self-examine their testicles for signs of cancer and little compliance with this behaviour. This sample reported more smoking and alcohol use than previously reported samples of American nurses and U.K. norms. The nurses in this sample were more likely to avoid foods high in cholesterol, add fibre to their diet and be more vigilant in their driving behaviour than American nurses and British non-nurses.  相似文献   
92.
Malignant mesothelioma is caused almost exclusively by occupational exposure to asbestos. During the past few years, however, increasing evidence has mounted that background exposure to asbestos could be sufficient to cause mesothelioma. Treatment of malignant mesothelioma remains a big problem. Some new approaches are on their way, and the most exciting ones are local immunotherapy in very early cases. Some success has been reported with local interferon treatment. As for treatment of metastatic pleural disease, the main purpose is symptomatic relief of dyspnea caused by fluid accumulation. The best way to achieve a lasting palliation is pleurodesis, and the most common way to do this, is by chemical means. The drug of choice in the United States has for many years been tetracycline, but since injectable tetracycline is no longer available, some substitute must be found. The substance that will "win" is not yet clear, but the two leading contestants are talc and doxycycline. Bleomycin also has its supporters, and a dark horse is quinacrine, which although not easily available in the United States, has been used in many European centers for decades.  相似文献   
93.
During the last few years, morphological, immunohistochemical, and genetic findings have placed anaplastic large cell lymphoma (ALCL) as a distinct clinicopathologic entity, and several reports have focused on the existence of different subtypes of the tumor. Particular attention has been paid to the ALCL-Hodgkin's-like (HL) subtype, which seems to be on the border between Hodgkin's disease (HD) and high-grade non-Hodgkin's lymphoma (HG-NHL). From September 1994 to July 1997, during the course of an Italian multicentric trial, 40 ALCL-HLs were randomized to receive as front-line chemotherapy MACOP-B (methotrexate with leucovorin, doxorubicin, cyclophosphamide, vincristine, prednisone, and bleomycin-a third-generation HG-NHL regimen) or ABVD (doxorubicin, bleomycin, vinblastine, and dacarbazine-a scheme specific for HD). All patients with bulky disease in the mediastinum at diagnosis underwent local radiotherapy after the chemotherapeutic program. Complete response (CR) was achieved in 17 of the 19 (90%) patients who were treated with MACOP-B, and in 19 of the 21 (91%) patients who were administered ABVD. The probability of relapse-free survival, projected at 32 months, was 94% for the MACOP-B subset and 91% for the ABVD subset. The majority of patients with mediastinal bulky disease obtained CR (evaluated with 67Ga single photon emission computed tomography [SPECT]) after their radiotherapy. The present study suggests that ALCL-HL, in line with its borderline status, responds in an equivalent way to third-generation chemotherapy for HG-NHL and to conventional HD treatment in terms of both CR and relapse-free survival rates. However, as to the latter, a longer follow-up period may be needed before stating the absolute equivalence of the two regimens used.  相似文献   
94.
We have directly determined the amide band resonance Raman spectra of the "average" pure alpha-helix, beta-sheet, and unordered secondary structures by exciting within the amide pi-->pi* transitions at 206.5 nm. The Raman spectra are dominated by the amide bands of the peptide backbone. We have empirically determined the average pure alpha-helix, beta-sheet, and unordered resonance Raman spectra from the amide resonance Raman spectra of 13 proteins with well-known X-ray crystal structures. We demonstrate that we can simultaneously utilize the amide I, II, and III bands and the Calpha-H amide bending vibrations of these average secondary structure spectra to directly determine protein secondary structure. The UV Raman method appears to be complementary, and in some cases superior, to the existing methods, such as CD, VCD, and absorption spectroscopy. In addition, the spectra are immune to the light-scattering artifacts that plague CD, VCD, and IR absorption measurements. Thus, it will be possible to examine proteins in micelles and other scattering media.  相似文献   
95.
OBJECTIVE: To determine the prevalence of suicidal ideation and the symptomatic profile as well as to identify the sociodemographic characteristics highlighting female adolescents with the highest scores on suicidal ideation in adolescents living in Mexico City: students and suicidal patients. MATERIAL AND METHODS: A cross-sectional and ex-post-facto study was carried out in order to analyze information from two samples: 1,712 junior and junior high school women students (representative student sample in Mexico City), and 30 adolescents inpatient hospitalized for her suicide attempts (clinical sample). RESULTS: Prevalence of presence as well as persistence of suicidal ideation were higher in the clinical sample, nevertheless 11.8% of the school sample had everyone of the symptoms in a range of 1 to 7 days. The most persistent of the ideation symptoms was: "My family would be better if I were dead"; and in the clinical sample it was "I thought about killing myself". Finally, the sociodemographic characteristics that best matched the student girls having the highest scores in suicidal ideation were: to be on junior high school, to get low grades, to acknowledge school performance as bad and to have interrupted her studies. The characteristics that highlight the girls with a first attempt were analyzed in the clinic sample in comparison with those ones with two or more attempts. It was significant that girls in the second group were living only with one parent and they thought in the last attempt that their dead would be possible or certain. CONCLUSIONS: The prevalence of suicidal ideation was important in the school sample. If it is considered that this psychological construct has a strong association with suicidal attempt, and multiple suicide conduct, then is a priority to detect adolescents in risk and to make preventive efforts, considering the sociodemographic characteristics that configurate in risk for suicidal ideation.  相似文献   
96.
Using loss of heterozygosity analysis, a method designed to detect moderate to large gene deletions, we have identified a new-mutation neurofibromatosis type 1 (NF1) patient who is somatically mosaic for a large maternally derived deletion in the NF1 gene region. The deletion extends at least from exon 4 near the 5' end of the gene to intron 39 near the 3' end. The gene-coding region is, therefore, mostly or entirely deleted, encompassing a loss of > or = 100 kb. We hypothesize that the deletion occurred at a relatively early developmental timepoint, since signs of NF1 in this patient are not confined to a specific body region, as seen in "segmental" NF, and since both mesodermally and ectodermally derived cells are affected. This report provides the first molecular evidence of somatic mosaicism in NF1 and, taken together with a recent report of germ-line mosaicism in NF1, adds credence to the concept that mosaicism plays an important role in phenotypic and genetic aspects of NF1 and may even be a relatively common phenomenon.  相似文献   
97.
垂直搜索是针对某一个行业的专业搜索引擎,是搜索引擎的细分和延伸,是对网页库中的某类专门的信息进行一次整合,定向分字段抽取出需要的数据进行处理后再以某种形式返回给用户。该文结合使用Heritrix与Lucene对学校新闻网站网页进行抓取并建立索引,建立相对应的新闻垂直搜索引擎系统。  相似文献   
98.
The number of people smoking free-base cocaine, or "crack," has increased dramatically in recent years. Concomitantly, the literature describing complications of such use has grown as well. Adverse pulmonary effects are being increasingly noted, such as respiratory symptoms, pulmonary hemorrhage, pulmonary edema, asthma, and pulmonary barotrauma. These and other pulmonary effects are reviewed.  相似文献   
99.
城市热岛效应作为城市化进程的负效应,其成因具有复杂性和地域性特征.以西安市为例,基于多元目标分析的主成分方法定量计算了不同影响因子对西安市热岛效应的贡献度大小,并以此为基础,最终筛选了城市人口、人均拥有道路面积、人均拥有机动车数、人均绿化面积、建成区面积、降水量及平均风速7个主要因素作为西安市热岛效应的主要成因;最后,从调整城市规划思路、控制工业热源、调控民用热源等三个方面为出发点构建了应对西安市热岛效应的宏观调控体系,其内容由3个一级指标、12个二级指标和5个三级指标构成.对应对和缓解西安市热岛效应具有积极的指导意义,也为其它城市应对热岛效应提供范式参考.  相似文献   
100.
Histological and histochemical techniques have been employed to determine the structure and autonomic innervation of paraganglia located in the human pelvis. In foetal and early postnatal tissues, paraganglia formed rounded cellular masses which were frequently in company with the autonomic nerves and ganglia of the urinary bladder and other pelvic viscera. The constituent cells contained only small amounts of cholinesterase and were unrelated to enzyme positive autonomic nerves; acetylcholinesterase containing nerves were occasionally observed in the capsule and the fibrous septa of the pelvic paraganglia. In early postnatal specimens, pelvic paraganglia frequently contained single or multiple "pacinian-like" corpuscles, each possessing a central region which was rich in both acetyl and pseudocholinesterase. These structures were rarely observed within autonomic ganglia and were absent 4 1/2 years post partum. By means of a histochemical technique, pelvic paraganglia were found to contain catecholamine which was attributed to the presence of relatively large quantities of noradrenaline. These observations have been discussed with particular reference to the results of other studies on the autonomic innervation of paraganglia.  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