全文获取类型
收费全文 | 4993篇 |
免费 | 252篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 82篇 |
综合类 | 20篇 |
化学工业 | 882篇 |
金属工艺 | 95篇 |
机械仪表 | 108篇 |
建筑科学 | 235篇 |
矿业工程 | 14篇 |
能源动力 | 148篇 |
轻工业 | 445篇 |
水利工程 | 38篇 |
石油天然气 | 49篇 |
无线电 | 552篇 |
一般工业技术 | 874篇 |
冶金工业 | 931篇 |
原子能技术 | 23篇 |
自动化技术 | 762篇 |
出版年
2023年 | 47篇 |
2022年 | 87篇 |
2021年 | 132篇 |
2020年 | 105篇 |
2019年 | 118篇 |
2018年 | 127篇 |
2017年 | 121篇 |
2016年 | 148篇 |
2015年 | 114篇 |
2014年 | 145篇 |
2013年 | 288篇 |
2012年 | 202篇 |
2011年 | 323篇 |
2010年 | 200篇 |
2009年 | 230篇 |
2008年 | 232篇 |
2007年 | 225篇 |
2006年 | 166篇 |
2005年 | 136篇 |
2004年 | 115篇 |
2003年 | 106篇 |
2002年 | 80篇 |
2001年 | 71篇 |
2000年 | 77篇 |
1999年 | 83篇 |
1998年 | 232篇 |
1997年 | 152篇 |
1996年 | 103篇 |
1995年 | 94篇 |
1994年 | 76篇 |
1993年 | 69篇 |
1992年 | 41篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 38篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 44篇 |
1984年 | 39篇 |
1983年 | 32篇 |
1982年 | 48篇 |
1981年 | 40篇 |
1980年 | 28篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 51篇 |
1976年 | 61篇 |
1975年 | 21篇 |
1974年 | 32篇 |
排序方式: 共有5258条查询结果,搜索用时 18 毫秒
21.
Jennings Kay D.; Harmon Robert J.; Morgan George A.; Gaiter Juarlyn L.; Yarrow Leon J. 《Canadian Metallurgical Quarterly》1979,15(4):386
To measure exploratory play at 1 yr of age, 41 middle-class infants were observed in a free-play setting. In a separate session, 11 structured tasks assessed the infants' persistence in mastering tasks. In a 3rd session, the Bayley Scales of Infant Development were given. As part of another study, home observations were available for 40 of the infants at 1 yr of age and for 23 of the infants at 6 mo of age. Measures of quantitative aspects of exploratory play showed no relationship to persistence or cognitive development; however, measures indexing the quality of exploratory play did. In addition, environmental measures at both 6 and 12 mo were related to exploratory play at 1 yr, particularly to the production of perceptual effects; but some of these findings were opposite to those expected. Results suggest that the quality of exploratory play, rather than the quantity, is a better index of underlying mastery motivation. In addition, the widely accepted assumption of a link between the amount of general exploration and cognitive ability needs to be reexamined. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
22.
Linear shape from shading 总被引:6,自引:1,他引:6
Alex P. Pentland 《International Journal of Computer Vision》1990,4(2):153-162
In many situations the reflectance function of a surface is approximately linear, and there is an effielent closed-form solution to the shape-from-shading problem. When boundary conditions (e.g., edges, singular points) are not available, good estimates of shape may still be extracted by using the assumption of general viewing position. An improved method for estimating the illuminant direction is also presented. 相似文献
23.
Grgoire B. Morand Isabel Cardona Sara Brito Silva Costa Cruz Alex M. Mlynarek Michael P. Hier Moulay A. Alaoui-Jamali Sabrina Daniela da Silva 《International journal of molecular sciences》2022,23(15)
The rise in human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC) has prompted a quest for further understanding of the role of high-risk HPV in tumor initiation and progression. Patients with HPV-positive OPSCC (HPV+ OPSCC) have better prognoses than their HPV-negative counterparts; however, current therapeutic strategies for HPV+ OPSCC are overly aggressive and leave patients with life-long sequalae and poor quality of life. This highlights a need for customized treatment. Several clinical trials of treatment de-intensification to reduce acute and late toxicity without compromising efficacy have been conducted. This article reviews the differences and similarities in the pathogenesis and progression of HPV-related OPSCC compared to cervical cancer, with emphasis on the role of prophylactic and therapeutic vaccines as a potential de-intensification treatment strategy. Overall, the future development of novel and effective therapeutic agents for HPV-associated head and neck tumors promises to meet the challenges posed by this growing epidemic. 相似文献
24.
Wenbo Zhou Julia Craft Alex Ojemann Luke Bergen Arin Graner Aitana Gonzales Qianbin He Timothy Kopper Marie Smith Michael W. Graner Xiaoli Yu 《International journal of molecular sciences》2022,23(13)
WHO Grade 4 IDH-wild type astrocytoma (GBM) is the deadliest brain tumor with a poor prognosis. Meningioma (MMA) is a more common “benign” central nervous system tumor but with significant recurrence rates. There is an urgent need for brain tumor biomarkers for early diagnosis and effective treatment options. Extracellular vesicles (EVs) are tiny membrane-enclosed vesicles that play essential functions in cell-to-cell communications among tumor cells. We aimed to identify epitopes of brain tumor EVs by phage peptide libraries. EVs from GBM plasma, MMA plasma, or brain tumor cell lines were used to screen phage-displayed random peptide libraries to identify high-affinity peptides. We purified EVs from three GBM plasma pools (23 patients), one MMA pool (10 patients), and four brain tumor cell lines. We identified a total of 21 high-affinity phage peptides (12 unique) specific to brain tumor EVs. The peptides shared high sequence homologies among those selected by the same EVs. Dose–response ELISA demonstrated that phage peptides were specific to brain tumor EVs compared to controls. Peptide affinity purification identified unique brain tumor EV subpopulations. Significantly, GBM EV peptides inhibit brain tumor EV-induced complement-dependent cytotoxicity (necrosis) in neurons. We conclude that phage display technology could identify specific peptides to isolate and characterize tumor EVs. 相似文献
25.
Alex A. Meier Eden P. Go Hee-Jung Moon Heather Desaire Minae Mure 《International journal of molecular sciences》2022,23(11)
Lysyl oxidase-like 2 (LOXL2) catalyzes the oxidative deamination of peptidyl lysines and hydroxylysines to promote extracellular matrix remodeling. Aberrant activity of LOXL2 has been associated with organ fibrosis and tumor metastasis. The lysine tyrosylquinone (LTQ) cofactor is derived from Lys653 and Tyr689 in the amine oxidase domain via post-translational modification. Based on the similarity in hydrodynamic radius and radius of gyration, we recently proposed that the overall structures of the mature LOXL2 (containing LTQ) and the precursor LOXL2 (no LTQ) are very similar. In this study, we conducted a mass spectrometry-based disulfide mapping analysis of recombinant LOXL2 in three forms: a full-length LOXL2 (fl-LOXL2) containing a nearly stoichiometric amount of LTQ, Δ1-2SRCR-LOXL2 (SRCR1 and SRCR2 are truncated) in the precursor form, and Δ1-3SRCR-LOXL2 (SRCR1, SRCR2, SRCR3 are truncated) in a mixture of the precursor and the mature forms. We detected a set of five disulfide bonds that is conserved in both the precursor and the mature recombinant LOXL2s. In addition, we detected a set of four alternative disulfide bonds in low abundance that is not associated with the mature LOXL2. These results suggest that the major set of five disulfide bonds is retained post-LTQ formation. 相似文献
26.
David S. Pisetsky Angel Garza Reyna Morgan E. Belina Diane M. Spencer 《International journal of molecular sciences》2022,23(9)
Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus, a prototypic autoimmune disease. These antibodies bind to conserved sites on single-stranded and double-stranded DNA and display variable region somatic mutations consistent with antigen selection. Nevertheless, the interaction of anti-DNA with DNA has unconventional features. Anti-DNA antibodies bind by a mechanism called monogamous bivalency, in which stable interaction requires contact of both Fab sites with determinants on the same extended DNA molecule; the size of this DNA can be hundreds to thousands of bases, especially in solid phase assays. This binding also requires the presence of the Fc portion of IgG, a binding mechanism known as Fc-dependent monogamous bivalency. As shown by the effects of ionic strength in association and dissociation assays, anti-DNA binding is primarily electrostatic. Like anti-DNA autoantibodies, anti-DNA antibodies that bind specifically to non-conserved sites on bacterial DNA, a type of anti-DNA found in otherwise healthy individuals, also interact by monogamous bivalency. The unconventional features of anti-DNA antibodies may reflect the highly charged and polymeric nature of DNA and the need for molecular rearrangements to facilitate monogamous bivalency; the Fc portion contributes to binding in an as yet unknown way. 相似文献
27.
This article describes some of the challenges of supporting older adults’ creative input to the design of an (as yet) undefined digital television application. Focusing on commonly used brainstorming and paper prototyping techniques, constructive insights are gathered from users with limited experience of interactive technology. Encouraging older participants to move beyond what they are familiar with, the research reports on how fragmented conceptual knowledge of familiar technologies can either facilitate or impede the creative development of new ideas. This includes bias or contradictory ideas that can emerge in the elicitation process. As reported, other factors, such as the self-perception of inadequate drawing skills, demonstrate further barriers for some older adults to articulate their visions and aspirations for suitably designed technology. 相似文献
28.
We argue that more help does not necessarily lead to more gratitude. Rather, gratitude depends on how a given instance of help compares with the help that a person is used to receiving. Participants read vignettes detailing an event in which 11 different friends either lent them varying amounts of money or spent varying amounts of time providing help. The amount of gratitude elicited by a given amount of help (e.g., a loan of £36 [about $56] or 49 min help) differed substantially depending on how this amount ranked among the help they were getting from their other friends. Comparison across four experimental conditions suggested that these judgments operated via the same general cognitive mechanisms used to judge other social events and psychophysical stimuli (as outlined by range frequency theory). Although more help does lead to more gratitude, people appear to be sensitive to how that help compares with what others are providing, and experienced gratitude depends on these relative judgments. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
29.
Research productivity affects the careers of academic psychologists. Unfortunately, there is a surprising lack of consensus on productivity’s meaning, measurement, and how to compare the productivity of one academic psychologist to another. In the present study, we review academic productivity research within psychology, and using a sample of 673 psychologists, compute six indexes of productivity. Most productivity metrics (publication count, citation count, or some combination of the two) were substantially interrelated and one (Integrated Research Productivity Index) was independent from years in the field. Female psychologists were equally as productive as male psychologists after accounting for years in the field, and pre-tenure psychologists showed steeper change-over-time productivity slopes than post-tenure psychologists. Based on these findings, we provide recommendations for the use and measurement of academic research productivity. 相似文献
30.