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   4017篇
  免费   16篇
  国内免费   1篇
电工技术   8篇
综合类   1篇
化学工业   70篇
金属工艺   8篇
机械仪表   9篇
建筑科学   23篇
能源动力   11篇
轻工业   68篇
水利工程   7篇
石油天然气   4篇
无线电   43篇
一般工业技术   65篇
冶金工业   3654篇
原子能技术   15篇
自动化技术   48篇
  2019年   6篇
  2018年   6篇
  2017年   8篇
  2016年   8篇
  2014年   10篇
  2013年   26篇
  2012年   7篇
  2011年   18篇
  2010年   17篇
  2009年   17篇
  2008年   21篇
  2007年   14篇
  2006年   18篇
  2005年   19篇
  2004年   5篇
  2003年   9篇
  2002年   13篇
  2001年   11篇
  2000年   18篇
  1999年   110篇
  1998年   984篇
  1997年   600篇
  1996年   391篇
  1995年   214篇
  1994年   204篇
  1993年   228篇
  1992年   43篇
  1991年   60篇
  1990年   63篇
  1989年   76篇
  1988年   71篇
  1987年   74篇
  1986年   58篇
  1985年   60篇
  1984年   8篇
  1983年   16篇
  1982年   24篇
  1981年   26篇
  1980年   38篇
  1979年   13篇
  1978年   16篇
  1977年   115篇
  1976年   235篇
  1975年   14篇
  1974年   5篇
  1973年   6篇
  1971年   3篇
  1965年   3篇
  1958年   2篇
  1955年   3篇
排序方式: 共有4034条查询结果,搜索用时 15 毫秒
41.
The goal of this research was to identify patients' preferences for physician inquiry into various aspects of health status and to examine whether the preconsultation availability of health status data (collected from the SF-36 Health Status Questionnaire) influenced the physician's conduct during the consultation. Results from 58 prenatal patient visits yielded the following findings. First, patients expressed strong preferences for physicians to ask about the patient's perceptions of health in general and about physical dimensions of health status such as pain, vitality, and role limitations due to physical functioning. Patients also were more satisfied when doctors were perceived as having asked about these issues. Second, patients varied considerably in their preferences for physician inquiries into psychosocial issues such as social functioning, mental health, and role limitations due to emotional problems. Approximately half the patients wanted these matters discussed, whereas the remainder either did not care or preferred that doctors not ask about these topics. Third, the preconsultation availability of health status information had little effect on the degree to which physicians asked about the patient's health-related quality of life. Clinical implications are discussed.  相似文献   
42.
STUDY OBJECTIVES: To define a set of orthostatic vital signs that minimize the frequency of false-positives among healthy individuals while maximizing sensitivity in detecting acute moderate blood loss and to determine the sensitivity and specificity of this optimized tilt test in detecting acute moderate blood loss. DESIGN AND INTERVENTION: Postural vital signs were recorded in a standardized manner before and after 450-mL phlebotomy. Paired comparisons were done for a variety of criteria for a positive tilt test using receiver-operating characteristic curves. SETTING AND TYPE OF PARTICIPANTS: Three hundred forty-five healthy euvolemic adult volunteer blood donors were tested at three community blood donation centers over a one-year period. Subjects were prospectively divided into group 1 (less than age 65; 301) and group 2 (age 65 or older; 44). MEASUREMENTS AND MAIN RESULTS: For each combination of pulse and blood pressure in group 1, a change in pulse alone had the same or higher sensitivity with at least the same specificity. Pulse alone was similarly superior in group 2 compared with previously published combinations of pulse and blood pressure. Even the optimized tilt test had limited sensitivity in detecting acute moderate blood loss with high specificity. CONCLUSION: In applying the tilt test to young adults without cardiovascular disease, pulse measurement usually is all that is necessary.  相似文献   
43.
Radiographic computed tomography and magnetic resonance imaging are the procedures of choice in the diagnosis of patients with suspected pituitary gland abnormalities. Several cases are presented where the diagnostic value of such procedures in patients with diseases affecting the pituitary gland is demonstrated.  相似文献   
44.
We established an in vitro model of the phagocytosis of Mycobacterium tuberculosis by human peripheral blood monocytes to evaluate the subsequent inhibition of intracellular replication of the organism. Highly purified T cells (94% CD3(+)/CD16(-)) or natural killer (NK) cells (96% CD16(+)/CD3(-)) isolated by Percoll discontinuous density gradient of peripheral blood mononuclear cells were incubated with M. tuberculosis-infected monocyte monolayers. Monocytes were lysed immediately and at 4, 7, and 10 d after infection for quantification of intracellular replication, which was assessed by quantitative plating techniques as colony-forming units (CFU). Whereas control monocytes permitted intracellular replication, T cells activated monocytes to kill 77% (p < 0.01) of intracellular M. tuberculosis compared with control monocytes by 10 d after infection. NK cells activated monocytes to kill 84% (p < 0.01) of M. tuberculosis in comparison with control monocytes. Lymphokine (IL-2)-activated-killer (LAK) cells were capable of activating monocytes to kill 97% (p < 0.01) of the intracellular organisms compared with control monocytes. In purified protein derivative (PPD)-positive donors, PPD-specific-CD4(+) lymphocytes stimulated monocytes to kill intracellular M. tuberculosis in a Class II major histocompatibility complex-restricted manner. In contrast, in PPD-negative donors, CD4(-) lymphocytes activated monocytes in a genetically unrestricted manner. Both T cell supernatant and NK cell supernatant generated from cocultivation with M. tuberculosis-infected monocytes also activated monocytes to augment mycobactericidal function. In conclusion, T cells, NK cells, LAK cells, and their supernatants activated mycobactericidal function of monocytes, although these pathways of activation differed in terms of antigenic specificity and genetic restriction.  相似文献   
45.
46.
Excretion was studied of catecholamines and diphenilamine (DOPA) in 310 patients with carcinoma of the stomach and large intestine and 43 patients with non-malignant diseases. The oncological patients showed decrease in activity of the mediator link of the sympathoadrenal system (SAS) as well as its reserves but there was no association with sex, age, location or histological structure. Three types of SAS functioning were identified, such as compensation, overstrain and emaciation. Surgical intervention led to activation of the hormonal link and exhaustion of the system's reserves. Two kinds of sympathoadrenal response to stress were described--adequate and inadequate. In the former type, phases of stress remain as they are, unchanged, as are time periods of formation thereof, while under the latter one time periods of the phases formation or formation thereof get disordered.  相似文献   
47.
Spin angular momentum conservation in chemiionization reactions involving optically oriented He(2(3)S) atoms in a flowing helium afterglow has been exploited to yield a source of spin-polarized electrons. Either transversely or longitudinally polarized electrons can be extracted. Polarized electron beam currents of approximately 2 muA have been realized at 40% polarization. The beam has an effective emittance of approximately 2 mrad/cm over the energy range 100-400 eV, an energy spread of less, similar0.15 eV, and the polarization is readily reversible. The source is relatively inexpensive and appears suitable for the majority of low-energy spin-dependent scattering experiments proposed to date.  相似文献   
48.
49.
Li and Tiwari (2008) recently developed a corrected Z-test statistic for comparing the trends in cancer age-adjusted mortality and incidence rates across overlapping geographic regions, by properly adjusting for the correlation between the slopes of the fitted simple linear regression equations. One of their key assumptions is that the error variances have unknown but common variance. However, since the age-adjusted rates are linear combinations of mortality or incidence counts, arising naturally from an underlying Poisson process, this constant variance assumption may be violated. This paper develops a weighted-least-squares based test that incorporates heteroscedastic error variances, and thus significantly extends the work of Li and Tiwari. The proposed test generally outperforms the aforementioned test through simulations and through application to the age-adjusted mortality data from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute.  相似文献   
50.
Twenty-two laboratories participated in a collaborative test to determine the iodine value (IV) of eight samples of fish oil (four with IV<150, four with IV>150) with either carbon tetrachloride (AOCS Official Method Cd 1–25) or cyclohexane (AOCS Recommended Practice Cd 1b-87) as solvent and either 1 or 2 h of reaction time. Laboratories received coded duplicate samples (hidden duplicates) and carried out duplicate determinations on each oil by each solvent-time combination (open duplicates). Replacing carbon tetrachloride with cyclohexane resulted in a lower IV (P<0.001). The decrease averaged 1.6 IV units for low-IV oils and 3.8 IV units for high-IV oils; this difference in response of 2.2 IV units between low- and high-IV oils was significant (P<0.001). Increasing the reaction time had a relatively small effect (0.34±0.18). There was no interaction of reaction time with solvent or oil type. Cyclohexane caused emulsions, which made it difficult to titrate residual iodine and thus increased the variability of the determination. The repeatability standard deviations (s r ), based on hidden duplicates, for 1-h reaction time with carbon tetrachloride and cyclohexane were 2.17 and 3.35, respectively. The corresponding reproducibility standard deviations were 2.73 and 4.53.  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