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   731246篇
  免费   9583篇
  国内免费   2886篇
电工技术   12773篇
综合类   3120篇
化学工业   106108篇
金属工艺   32739篇
机械仪表   25459篇
建筑科学   16554篇
矿业工程   4284篇
能源动力   18385篇
轻工业   50823篇
水利工程   8141篇
石油天然气   13250篇
武器工业   56篇
无线电   85286篇
一般工业技术   148214篇
冶金工业   121512篇
原子能技术   15179篇
自动化技术   81832篇
  2021年   5798篇
  2020年   4314篇
  2019年   5504篇
  2018年   25745篇
  2017年   25039篇
  2016年   20729篇
  2015年   7171篇
  2014年   10843篇
  2013年   29683篇
  2012年   20793篇
  2011年   35098篇
  2010年   29205篇
  2009年   28917篇
  2008年   30153篇
  2007年   31810篇
  2006年   18533篇
  2005年   19710篇
  2004年   17999篇
  2003年   17634篇
  2002年   15892篇
  2001年   15034篇
  2000年   14265篇
  1999年   14802篇
  1998年   37446篇
  1997年   26078篇
  1996年   20030篇
  1995年   15062篇
  1994年   13192篇
  1993年   13313篇
  1992年   9510篇
  1991年   9024篇
  1990年   8842篇
  1989年   8533篇
  1988年   8027篇
  1987年   7093篇
  1986年   7037篇
  1985年   7829篇
  1984年   7168篇
  1983年   6559篇
  1982年   6091篇
  1981年   6194篇
  1980年   5927篇
  1979年   5601篇
  1978年   5609篇
  1977年   6358篇
  1976年   8347篇
  1975年   4756篇
  1974年   4573篇
  1973年   4688篇
  1972年   3928篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.  相似文献   
984.
PMGDM, a PMDM-type adhesive monomer, was synthesized from pyromellitic dianhydride and glycerol dimethacrylate. Only the para isomer of PMDM, a solid, is used in dental adhesives. The adhesive monomer PMGDM is a liquid and consists of a mixture of para- and meta isomers. This study shows that PMGDM has several advantages over PMDM. For example, the adhesive can be applied at a greater thickness, and additives and/or additional initiators for improved curing can be incorporated. Use of the liquid monomer PMGDM also provided a convenient means of varying the thickness of the adhesive layer between dentin and composite. The adhesive bonds were tested in both shear and tensile modes. PMDM was used as the control. The reliability of the bonds, as judged from the Weibull modulus and Weibull characteristic strength, was improved by (1) use of more concentrated solutions of PMGDM adhesive, (2) use of an adhesive thickness of about 25 microns, and (3) modification of PMGDM with a diluent monomer which is expected to enhance the degree of cure and/or the dentin-wetting properties of the adhesive resin.  相似文献   
985.
The lingual serous glands of von Ebner are located close to the foliate and circumvallate papillae. Saliva secreted by these glands provides the immediate environment of the taste buds, and it has been hypothesized that it modulates taste perception. The purpose of this study was to develop a technique for collection of unstimulated and stimulated saliva from human von Ebner glands. Saliva was collected under resting conditions and after application of various gustatory stimuli (sweet, sour, salt, and bitter) by insertion of periostrips into the folds of the foliate papillae of healthy human volunteers. Stimulated saliva was also collected in glass microcapillaries or micropipettes. The flow-rates of unstimulated von Ebner saliva were 2.3 +/- 0.6 (S.E.) microL/min and 4.5 +/- 1.2 (S.E.) microL/min with 1% citric acid stimulation. The protein content was 2.5 +/- 0.5 (S.E.) mg/mL. The SDS gel electrophoretic profile of von Ebner saliva revealed two protein bands of Mr 18,000 that were identified on Western blots as von Ebner gland (VEG) proteins. Although lingual lipase activity was detected at very low levels by enzyme assay, this protein was not detected on Western blots. This collection technique should prove useful for analysis of specific functions associated with secretion from von Ebner glands.  相似文献   
986.
987.
This report details procedures to measure annihilation anxiety, a concept derived from Freud's 1926 formulation of traumatic anxiety. A 25-item pencil-and-paper inventory administered to patient and to nonpatient samples is described, along with a brief summary of earlier findings. The delineation of nine interrelated experiential components of annihilation anxiety provides the background for the construction of Rorschach and TAT measures of the concept. Findings comparing the pencil-and-paper inventory and the projective test measures are presented as well as examples of responses judged to reflect annihilation anxiety from Rorschach and TAT protocols.  相似文献   
988.
Growth hormone (GH) has recently been shown to affect polymorphonuclear neutrophil granulocyte (PMN) function and to be secreted by mononuclear cells, indicating that the hormone may be active in an immunophysiologic network, acting as an endo- or paracrine priming agent. The purpose of the present study was to evaluate the chemotactic responsiveness of canine peripheral PMN in a dog with acromegaly, caused by spontaneous, progesterone-induced hypersecretion of GH and, secondary to this, a seven-fold increase in insulin-like growth factor I (IGF-I). The chemotactic responsiveness towards zymosan-activated serum (ZAS) and leukotriene B4 (LTB4) was evaluated at a time when the dog suffered from acromegaly and again 57 days after corrective surgery (ovariohysterectomy). The experiments showed that PMN from the patient exhibited enhanced chemotactic migration that appeared to be associated with the hypersomatotropic condition as judged from the reversibility of the phenomenon. The glucose intolerance and elevated serum alkaline phosphatase that were observed in the acromegalic dog were also shown to be reversible following surgery.  相似文献   
989.
The effects of adenosine and sodium nitroprusside (SNP) on central hemodynamics and myocardial blood flow and metabolism were investigated postoperatively after elective coronary artery bypass (CABG) surgery in ten sedated and mechanically ventilated patients in the intensive care unit. During three consecutive 15-min periods, SNP (0.8 +/- 0.1 micrograms.kg-1 x min-1), adenosine (88.9 +/- 13.3 micrograms.kg-1 x min-1), and then again SNP (0.7 +/- 0.1 micrograms.kg-1 x min-1) were infused to control postoperative hypertension at a mean arterial pressure of approximately 80 mm Hg. Systemic and pulmonary hemodynamics and global (coronary sinus flow, CSF) as well as regional (great cardiac vein flow, GCVF) myocardial blood flow and metabolic variables were measured. During adenosine infusion, in comparison to SNP, heart rate was unchanged, stroke volume index and cardiac index increased (24% and 32%, respectively), and the systemic vascular resistance index decreased (-26%). Mean pulmonary arterial pressure (24%) as well as pulmonary capillary wedge pressure (27%) and central venous pressure (18%) were higher with adenosine compared to SNP. Adenosine also increased CSF and GCVF (108% and 103%, respectively) without altering the CSF/GCVF flow ratio compared to SNP. Furthermore, adenosine increased the coronary oxygen content (51%) and decreased the arterio-great cardiac vein oxygen content difference (-48%) without changing regional myocardial oxygen consumption, indicating a more pronounced hyperkinetic myocardial circulation compared to SNP. In addition, adenosine infusion decreased arterial PO2 (-11%) and increased the intrapulmonary shunt fraction (57%). The PR interval time of the electrocardiogram was prolonged (12%) and the ST segment was more depressed during adenosine infusion compared to SNP.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
990.
Synergism between recombinant human tumour necrosis factor (rHuTNF) and DNA topoisomerase II inhibitor VP16 during the killing of cells has been studied in six human ovarian cancer cell lines (A2774, A2780, SW626, IGROV-1, SKOV3, Pa1) and a cervical carcinoma cell line (Me180). Studies were performed using an assay of colony formation inhibition (drug treatment for 1 h) and a growth inhibition assay (continuous exposure for 20 h). Concomitant treatment of cells with VP16+rHuTNF enhanced cell killing in all the cell lines tested--an effect observed in both short- and long-term cytotoxicity assays. This study suggests that the activity of VP16 in ovarian cancer cell lines might be enhanced by rHuTNF in in vitro models.  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