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   6065篇
  免费   18篇
  国内免费   4篇
电工技术   43篇
综合类   3篇
化学工业   476篇
金属工艺   113篇
机械仪表   67篇
建筑科学   146篇
矿业工程   9篇
能源动力   62篇
轻工业   336篇
水利工程   28篇
石油天然气   5篇
无线电   267篇
一般工业技术   421篇
冶金工业   3705篇
原子能技术   29篇
自动化技术   377篇
  2022年   22篇
  2021年   26篇
  2020年   32篇
  2019年   29篇
  2018年   25篇
  2017年   42篇
  2016年   33篇
  2015年   20篇
  2014年   35篇
  2013年   145篇
  2012年   66篇
  2011年   109篇
  2010年   78篇
  2009年   89篇
  2008年   107篇
  2007年   102篇
  2006年   89篇
  2005年   99篇
  2004年   79篇
  2003年   80篇
  2002年   89篇
  2001年   64篇
  2000年   63篇
  1999年   170篇
  1998年   1117篇
  1997年   627篇
  1996年   420篇
  1995年   256篇
  1994年   219篇
  1993年   255篇
  1992年   70篇
  1991年   66篇
  1990年   77篇
  1989年   75篇
  1988年   65篇
  1987年   72篇
  1986年   74篇
  1985年   90篇
  1984年   66篇
  1983年   45篇
  1982年   47篇
  1981年   53篇
  1980年   50篇
  1979年   33篇
  1978年   35篇
  1977年   101篇
  1976年   228篇
  1975年   29篇
  1974年   26篇
  1972年   21篇
排序方式: 共有6087条查询结果,搜索用时 0 毫秒
31.
This study was concerned with psychotherapists' evaluations of the outcome of therapy. Staff and resident psychiatrists employed in 23-item questionnaire to rate the seccess of psychotherapy with 85 of their inpatients. These were patients for whom psychotherapy constituted a significant part of the treatment that they received in the hospital. The therapists' responses to the questionnaire items were intercorrelated. The results indicated that a major aspect of a psychotherapist's judgment of the success of treatment-as these judgments usually are employed in current psychotherapy research-is the therapist's affective reaction to the patient, Better-liked patients were viewed as having improved more. However, when the therapists' responses were subjected to factor analysis, independent Improvement and Affection factors emerged. It is suggested that when therapists' ratings of success are used in psychotherapy research they should be treated or refined statistically to minimize potential confounding with their affection for patients.  相似文献   
32.
Conducted a study with 32 13-17 yr old male chronic truants from a low-income, inner-city area. Ss were given counseling aimed at returning them to regular attendance. Optimistic vs threat appeal and presence vs absence of supportive instruction were manipulated in a 2 * 2 design, and persuasion was assessed both as verbal intention to attend school regularly and as actual attendance. Supportive instruction included the continuing availability of a tutor. Results show that threat appeal was sufficient to change intention to return to school, but supportive instruction was necessary to change actual attendance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
33.
Hemangioma of scrotum   总被引:1,自引:0,他引:1  
  相似文献   
34.
Using light and electron microscopic morphometric techniques, the effects of 48 hr of extrahepatic biliary obstruction on hepatocyte structure were examined in the rat. Liver cells near the portal area were compared to those in the centrilobular regions of the hepatic lobule. Observations on the normal animals confirm earlier evidence of quantitative differences in the surface density of organelles in hepatocytes located within different regions of the lobule. A striking difference in the quantity of the Golgi complex in the two areas of the lobule was noted for the first time, with the portal cells containing a significantly greater quantity of this organelle than centrolobular hepatocytes. After 48 hr of total obstruction, most of the previously reported qualitative changes in the canalicular and pericanalicular regions were confirmed. Morphometric analysis at the light-microscopic level showed an increase in the number of cells and a decrease in cell size in those cells near the portal area were compared to those in the centrolobular regions of the helar level demonstrated a significant decrease in both rough and smooth surfaced endoplasmic reticulum in cells of both zones, a finding in marked contrast to the hypertrophy of smooth endoplasmic reticulum suggested by other investigators on the basis of qualitative assessments. There was also a striking decrease in the amount of the Golgi complex, limited to cells in the portal regions. In addition, in all zones a decrease in the volume density of mitochondria and lysosomes was noted, whereas the volume of microbodies was increased. It is suggested that this loss in total membrane material within the cell may be secondary to the degranulation and decrease in total surface area of rough surfaced endoplasmic reticulum, an organelle thought to be responsible in part for the synthesis of new cellular membranes. These observations suggest that present concepts concerning the pathogenesis of cholestatic liver disease require reappraisal.  相似文献   
35.
On examination of the thumbs of 20 dissected preparations of ligaments and joints, of ten dry skeletons and of a number of living hands, apoposition (from apo = away from) was distinguished as a position in which the first carpometacarpal joint is fully abducted and laterally rotated and in which one or both distal joints of the thumb are flexed. Apoposition is commonly used in writing and it has a specific osteoligamentous basis for its stability: (1) a Y-shaped intermetacarpal ligament is attached by two crura to the base of the second metacarpal bone and by a common stem to the first metacarpal. Together with the palmar and dorsal oblique ligaments it becomes taut at abduction and establishes thereby a fixed center for the circumduction. Stability is enhanced as the circumduction takes place in the radial flat part of the joint away from the center; (2) of the two palmar prominences of the head of the first metacarpal bone the radial is the larger. At 25-30 degrees flexion in the metacarpophalangeal joint the prominence fits into an excavation on the base of the proximal phalanx in a manner which together with the ulnar collateral ligament locks the joint against mutual abduction and lateral rotation, and (3) the radial part of the trochlea of the interphalangeal joint is larger than the ulnar and secures, together with the ulnar collateral ligament, the joint against a radial luxation. Apoposition does not require activity of the thumb muscles; it is brought about by applying an external force to the ulnar side of the thumb and it is checked by ligaments and the shape of the joints.  相似文献   
36.
Members of the immediate families of twenty children with specific reading disability were examined to determine the prevalence of reading disability within the families. A procedure was developed for identifying adults who may have compensated for a disability manifested more clearly in childhood. Forty-five percent of 75 first-degree relatives of the parents were affected and there was a significantly greater number of affected male relatives than females. No single mode of genetic transmission is evident after inspection of the pedigrees. It is suggested that the disorder is genetically heterogeneous and that subgroups of disabled readers should be looked for.  相似文献   
37.
There are two forms of ornithine decarboxylase with respect to pyridoxal 5'-phosphate (pyridoxal-P) affinity in exponentially-growing Swiss 3T3 mouse fibroblasts: form I (Km approximately 10 muM) accounts for 30% of the total activity, and form II (Km approximately 0.4 muM) the remainder. Each form of the enzyme is in rapid equilibrium with ornithine and pyridoxal-P; neither form recognizes the Schiff base between ornithine and pyridoxal-P as a substrate. Total pyridoxal-P concentrations indicate that both forms may normally be at least partially active in vivo. Upon stimulation of 3T3 cells by pituitary growth factors, form I becomes undetectable within 4 h. As total activity increases over 10-fold during this time and continues to increase thereafter, a possible conversion of form I to form II could account for this increase only if the Km change reflects other changes in preexisting enzyme. The rates of cofactor dissociation are apparently the same for each form and neither rate changes with the growth state. Since rapid equilibrium kinetics apply, the forms apparently differ in their rate of cofactor association. The half-lives of the two forms in vivo are the same in unstimulated cells when measured concurrently. Also, the half-life of total activity decreases markedly upon stimulation as form II becomes dominant. These and other observations are not consistent with pyridoxal-P serving a major protective function for the enzyme in vivo.  相似文献   
38.
Hartnup disease is a rare genetic disorder of amino acid transport associated with variable and intermittent clinical abnormalities. A family is described in which three siblings had an intermittently progressive neurological disease and two of the affected siblings had the Hartnup-pattern aminoaciduria. Neuropathological examination of one case showed severe diffuse atrophy, generalized neuronal loss in the cortex, and Purkinje cell loss in the cerebellum. In vivo and in vitro studies of intestinal amino acid transport in the surviving sibling indicated a partial defect in the transport of several neutral amino acids (tryptophan, alanine, serine, and methionine) with normal transport of other neutral amino acids (threonine, phenylalanine, histidine, tyrosine, and isoleucine). Transport of glycine, proline, hydroxyproline, and the basic amino acids appeared normal.  相似文献   
39.
Inconsistent evidence of inflammatory immune cell infiltrates in adipose tissues with extensive triglyceride mobilization raises the possibility that regulatory or anti-inflammatory immune cell populations reside within the mesenteric adipose tissue (MAT) and mesenteric lymph nodes (MLN). These resident immune cell populations may be involved in attenuating the inflammatory response. We explored the immune cell population of MAT and MLN collected from lean, lactating Holstein cows without apparent disease in an abattoir (n = 42). Lean cows had a body condition score of 2.6 ± 0.1 (mean ± SD) with a greater frequency of adipocyte area occurring in small rather than large adipocytes. Cells were labeled with monoclonal antibodies specific to bovine leukocyte antigens for enumeration by flow cytometry. Within both lymph node and adipose tissues, relatively large subpopulations of cells expressed the β2 integrins CD11b and CD11c, class II major histocompatibility antigens (MHCII), and the SIIRP-1α receptor (CD172a) typical of dendritic cells and macrophages. Macrophage/dendritic cell heterogeneity was marked by β2 integrin expression alone or in conjunction with CD172a or MHCII across subpopulations from both tissues; CD209, the DC-SIGN c-type lectin receptor of dendritic cells, was not detected by fluorescence-activated cell sorting in either tissue. Lymphocytes comprised 74.1 ± 3.7% and 13.7 ± 3.7% of the MLN and MAT cell populations, respectively, and CD3+CD4+ lymphocytes accounted for 49.8 ± 9.9% of the MLN and 6.13 ± 1.23% of the MAT cells. Fox P3+ regulatory lymphocytes comprised 15.3 ± 1.1% and 6.73 ± 0.52% of the MLN and MAT cells, whereas γδ+ lymphocytes accounted for 6.65 ± 0.74% and 3.91 ± 0.43% of the MLN and MAT cells, respectively. Subpopulations of CD3+CD8+ cytotoxic T cells and CD3+CD11c+ innate lymphocytes were present in MLN but not MAT. These results show that subpopulations of resident tissue macrophages, dendritic cells, T helper lymphocytes, regulatory T lymphocytes (Tregs), and γδ lymphocytes reside in mesenteric lymph nodes and adipose tissues. Balance in the innate and adaptive immune functions embedded in these tissues could support metabolic health.  相似文献   
40.
Mammalian vocalizations can encode contextual information in both the spectrographic components of their individual vocal units and in their temporal organization. Here we observed 23 Holstein-Friesian dairy cows immediately after birth during interactions with their calf and when their calf was separated to the other side of a fence line. We investigated whether the vocalizations emitted in these postpartum contexts would vary temporally. We also described the maternal and stress behaviors preceding and following postpartum vocal production using kinematic diagrams and characterized call sequence structure. The kinematic diagrams highlight the disruption of maternal responses caused by calf separation and show that behavioral and vocal patterns varied according to the cows' emotional states and proximity to the calf in both contexts. During calf interactions, cows mainly produced closed-mouth calls simultaneous to licking their calf, whereas an escalation of stress responses was observed during calf separation, with the cows approaching the fence line, becoming alert to the calf, and emitting more mixed and open-mouth calls. Call sequences were similarly structured across contexts, mostly containing repetitions of a single call type, with a mean interval of 0.57 s between calls and a greater cumulative vocalization duration, attributed to an increased number of vocal units per sequence. Overall, calf separation was associated with a greater proportion of calls emitted as a sequence (inverse of single isolated calls), a shorter interval between separate call sequences, and a greater number of vocal units per sequence, compared with calf interactions. These temporal vocal features varied predictably with the high stress expression from cows during calf separation and may represent temporal modulations of emotional expression. Despite the noisy farm soundscape, empirical call type and temporal vocal features were easy to measure; thus, findings could be applied to future cattle studies wishing to analyze vocalizations for on-farm welfare assessments.  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