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   3719篇
  免费   19篇
  国内免费   1篇
电工技术   8篇
综合类   1篇
化学工业   90篇
金属工艺   8篇
机械仪表   13篇
建筑科学   25篇
矿业工程   3篇
能源动力   14篇
轻工业   103篇
水利工程   3篇
无线电   56篇
一般工业技术   92篇
冶金工业   3273篇
原子能技术   6篇
自动化技术   44篇
  2021年   5篇
  2020年   11篇
  2019年   10篇
  2017年   9篇
  2016年   10篇
  2015年   6篇
  2014年   11篇
  2013年   35篇
  2012年   17篇
  2011年   16篇
  2010年   12篇
  2009年   11篇
  2008年   25篇
  2007年   16篇
  2006年   8篇
  2005年   11篇
  2004年   14篇
  2003年   20篇
  2002年   11篇
  2001年   21篇
  2000年   13篇
  1999年   118篇
  1998年   1015篇
  1997年   580篇
  1996年   355篇
  1995年   229篇
  1994年   175篇
  1993年   191篇
  1992年   25篇
  1991年   52篇
  1990年   45篇
  1989年   52篇
  1988年   60篇
  1987年   57篇
  1986年   41篇
  1985年   29篇
  1984年   10篇
  1983年   11篇
  1982年   21篇
  1981年   21篇
  1980年   33篇
  1979年   16篇
  1978年   15篇
  1977年   79篇
  1976年   163篇
  1974年   4篇
  1973年   5篇
  1970年   5篇
  1968年   4篇
  1967年   5篇
排序方式: 共有3739条查询结果,搜索用时 296 毫秒
71.
72.
This study examined the prevalence, comorbidity, and clinical correlates of personality disorders in an outpatient sample (N = 352) with anxiety and depression. Subjects were diagnosed using the Structured Clinical Interview for DSM-III-R (SCID) on Axes I and II, and they also completed interview and self-report measures of symptoms. Subjects with a personality disorder were less likely to be married, more likely to be single or divorced, had lower family incomes, had more severe symptoms of both anxiety and depression, and had a greater number of lifetime Axis I diagnoses. Subjects with dysthymic and bipolar disorders were more likely, and subjects with panic disorder uncomplicated by agoraphobia were less likely to have a personality disorder compared to the rest of the sample. The most prevalent personality disorders were Avoidant, Obsessive-Compulsive, Paranoid, and Borderline. Paranoid co-occurred with Narcissistic, and Borderline co-occurred with Histrionic personality disorder significantly more often than chance and base rates would predict.  相似文献   
73.
74.
OBJECTIVE: To determine the relative influences of induction of withdrawal bleedings secretory transformation, and reduction of mitosis in glands on prevention of endometrial hyperplasia during long-term hormonal replacement therapy. DESIGN: Observational expanded clinical case report. SETTING: Reproductive Endocrine Department of Hospital Necker, Paris, France, and Pathology Department of Women's Hospital, Los Angeles County and University of Southern California Medical Center, Los Angeles, California. PATIENTS: Postmenopausal women seeking treatment for symptomatic menopause. INTERVENTIONS: Endometrial biopsy and/or ambulatory hysteroscopy. MAIN OUTCOME MEASURE: Endometrial histology including progestational maturation patterns and glandular epithelial mitosis rates. Macroscopic endometrial appearance. RESULTS: The use of larger doses of E2 and P induced more marked secretory changes and more frequent withdrawal bleeding than the lower doses. There was no evidence of endometrial hyperplasia after 5 years of E2/P replacement therapy independently of bleeding pattern or progestational maturation. Consistent reduction of mitosis rates in glandular epithelium was found after 9 or more days of P administration in each cycle. CONCLUSIONS: Control of endometrial growth is mainly related to control of mitosis in glands by a relatively low doses of P. Induction of withdrawal bleeding and endometrial secretory transformation, which require larger doses of Progesterone, do not provide additional benefit for prevention of hyperplasia. Induction of amenorrhea with a relatively low dose of P may be offered to women seeking hormone replacement therapy with similar levels of safety.  相似文献   
75.
Thrombopoietin (TPO) has recently been cloned and shown to regulate megakaryocyte and platelet production by activating the cytokine receptor c-mpl. To determine whether TPO is the only ligand for c-mpl and the major regulator of megakaryocytopoiesis, TPO deficient mice were generated by gene targeting. TPO-/- mice have a >80% decrease in their platelets and megakaryocytes but have normal levels of all the other hematopoietic cell types. A gene dosage effect observed in heterozygous mice suggests that the TPO gene is constitutively expressed and that the circulating TPO level is directly regulated by the platelet mass. Bone marrow from TPO-/- mice have decreased numbers of megakaryocyte-committed progenitors as well as lower ploidy in the megakaryocytes that are present. These results demonstrate that TPO alone is the major physiological regulator of both proliferation and differentiation of hematopoietic progenitor cells into mature megakaryocytes but that TPO is not critical to the final step of platelet production.  相似文献   
76.
SR proteins are required for constitutive pre-mRNA splicing and also regulate alternative splice site selection in a concentration-dependent manner. They have a modular structure that consists of one or two RNA-recognition motifs (RRMs) and a COOH-terminal arginine/serine-rich domain (RS domain). We have analyzed the role of the individual domains of these closely related proteins in cellular distribution, subnuclear localization, and regulation of alternative splicing in vivo. We observed striking differences in the localization signals present in several human SR proteins. In contrast to earlier studies of RS domains in the Drosophila suppressor-of-white-apricot (SWAP) and Transformer (Tra) alternative splicing factors, we found that the RS domain of SF2/ASF is neither necessary nor sufficient for targeting to the nuclear speckles. Although this RS domain is a nuclear localization signal, subnuclear targeting to the speckles requires at least two of the three constituent domains of SF2/ASF, which contain additive and redundant signals. In contrast, in two SR proteins that have a single RRM (SC35 and SRp20), the RS domain is both necessary and sufficient as a targeting signal to the speckles. We also show that RRM2 of SF2/ASF plays an important role in alternative splicing specificity: deletion of this domain results in a protein that, although active in alternative splicing, has altered specificity in 5' splice site selection. These results demonstrate the modularity of SR proteins and the importance of individual domains for their cellular localization and alternative splicing function in vivo.  相似文献   
77.
78.
We found that the total watery extracts obtained from roots of various plants such as Symphytum officinale, Phytolacca americana etc, precipitate human glycoproteins, agglutinate sheep red blood cells (SRBC) and stimulate lymphocyte adherence to nylon fibers. Five out of seven extracts precipitated human gammaglobulins and one of seven obviously agglutinate SRBC. If these cells were pretreated with rabbit antibodies against SRBC, all extracts agglutinated the cells at various degrees of intensity, the most active being Phytolacca americana. The adherence of mouse but not human lymphocytes to nylon fibers was stimulated by extracts of Symphytum officinale and Phytolacca americana. This process was neither stimulated nor inhibited by Mannose (Man), Galactose (Gal), Glucose (Glc), N-acethyl Galactose (GalNAc) and N-acethyl Glucose (Glc-NAc). These biological effects of the plant extracts could be the expression of a lectin-like ability to bind various sugars other than those mentioned. The results suggest the possibility of using different extracts as means to point out the presence in serum or at the cellular level of some carbohydrates influencing the cellular adhesion, phenomenon which plays an important role in the functions of hematopoietic cells.  相似文献   
79.
80.
Multiple trials using antiarrhythmic drugs, pharmacologic therapy, and implantable cardioverter defibrillators have been performed in an attempt to improve survival in patients: (1) postmyocardial infarction; (2) with congestive heart failure, with and without nonsustained ventricular tachycardia; and (3) with sustained ventricular tachycardia and those who have survived an out-of-hospital cardiac arrest. This article reviews some of the key findings and limitations of completed and ongoing trials. We also make recommendations for the current treatment of such patients based on the results of these trials.  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