全文获取类型
收费全文 | 1341篇 |
免费 | 46篇 |
专业分类
化学工业 | 211篇 |
金属工艺 | 6篇 |
机械仪表 | 13篇 |
建筑科学 | 52篇 |
能源动力 | 13篇 |
轻工业 | 166篇 |
水利工程 | 11篇 |
石油天然气 | 6篇 |
无线电 | 57篇 |
一般工业技术 | 168篇 |
冶金工业 | 576篇 |
原子能技术 | 1篇 |
自动化技术 | 107篇 |
出版年
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 26篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 24篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 63篇 |
2012年 | 46篇 |
2011年 | 75篇 |
2010年 | 55篇 |
2009年 | 44篇 |
2008年 | 68篇 |
2007年 | 61篇 |
2006年 | 47篇 |
2005年 | 43篇 |
2004年 | 60篇 |
2003年 | 45篇 |
2002年 | 46篇 |
2001年 | 31篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 33篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 31篇 |
1994年 | 32篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 15篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有1387条查询结果,搜索用时 15 毫秒
61.
Birgit J.M. Hausmann Mughees Khan Yinan Zhang Tom M. Babinec Katie Martinick Murray McCutcheon Phil R. Hemmer Marko Lončar 《Diamond and Related Materials》2010,19(5-6):621-629
We present a design and a top-down fabrication method for realizing diamond nanowires in both bulk single crystal and polycrystalline diamond. Numerical modeling was used to study coupling between a Nitrogen Vacancy (NV) color center and optical modes of a nanowire, and to find an optimal range of nanowire diameters that allows for large collection efficiency of emitted photons. Inductively coupled plasma (ICP) reactive ion etching (RIE) with oxygen is used to fabricate the nanowires. Drop-casted nanoparticles (including Au, SiO2 and Al2O3) as well as electron beam lithography defined spin-on glass and evaporated Au have been used as an etch mask. We found Al2O3 nanoparticles to be the most etch resistant. At the same time FOx e-beam resist (spin-on glass) proved to be a suitable etch mask for fabrication of ordered arrays of diamond nanowires. We were able to obtain nanowires with near-vertical sidewalls in both polycrystalline and single crystal diamond. The heights and diameters of the polycrystalline nanowires presented in this paper are ≈ 1 μm and 120–340 nm, respectively, having a 200 nm/min etch rate. In the case of single crystal diamond (types Ib and IIa) nanowires the height and diameter for different diamonds and masks shown in this paper were 1–2.4 μm and 120–490 nm with etch rates between 190 and 240 nm/min. 相似文献
62.
63.
Jordan K. Vance Travis W. Rawson Jessica M. Povroznik Kathleen M. Brundage Cory M. Robinson 《International journal of molecular sciences》2021,22(13)
Neonates are at an increased risk of an infectious disease. This is consistent with an increased abundance of myeloid-derived suppressor cells (MDSCs) compared with older children and adults. Using a murine model of neonatal bacterial sepsis, we demonstrate that MDSCs modulate their activity during an infection to enhance immune suppressive functions. A gene expression analysis shows that MDSCs increased NOS2, Arg-1 and IL-27p28 expression in vitro and in vivo in response to Escherichia coli O1:K1:H7 and this is regulated at the level of the gene expression. Changes in the effector gene expression are consistent with increased enzymatic activity and cytokine secretion. The neonatal MDSCs express toll-like receptor (TLR) 2, 4 and 5 capable of recognizing pathogen-associated molecular patterns (PAMPS) on E. coli. However, a variable level of effector expression was achieved in response to LPS, peptidoglycan or flagellin. Individual bacterial PAMPs did not stimulate the expression of Arg-l and IL-27p28 equivalently to E. coli. However, the upregulation of NOS2 was achieved in response to LPS, peptidoglycan and flagella. The increased immune suppressive profile translated to an enhanced suppression of CD4+ T cell proliferation. Collectively, these findings increase our understanding of the dynamic nature of MDSC activity and suggest that these cells abundant in early life can acquire activity during an infection that suppresses protective immunity. 相似文献
64.
Wright Kathleen M.; Cabrera Oscar A.; Bliese Paul D.; Adler Amy B.; Hoge Charles W.; Castro Carl A. 《Canadian Metallurgical Quarterly》2009,6(2):108
The present study examined the effects of leadership and unit cohesion on mental health stigma and perceived barriers to care. A sample of 680 soldiers from combat support units were surveyed 3 months after their return from combat operations in Iraq. The survey included scales on psychological symptoms and perceptions of leader behaviors and unit cohesion, as well as items assessing stigma and barriers to care. The sample was used to test the independent and interactive effects of leadership and unit cohesion on soldiers’ perceptions of stigma and barriers to care. Analyses yielded significant interaction effects between leadership and cohesion in predicting stigma and barriers to care, while controlling for the effects of mental health symptoms. Soldiers who rated their leaders more highly and who reported higher unit cohesion also reported lower scores on both stigma and perceived barriers to care. Thus, positive leadership and unit cohesion can reduce perceptions of stigma and barriers to care, even after accounting for the relationship between mental health symptoms and these outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
65.
Ashenfelter Kathleen T.; Boker Steven M.; Waddell Jennifer R.; Vitanov Nikolay 《Canadian Metallurgical Quarterly》2009,35(4):1072
This study examined the influence of sex, social dominance, and context on motion-tracked head movements during dyadic conversations. Windowed cross-correlation analyses found high peak correlation between conversants’ head movements over short (≈2-s) intervals and a high degree of nonstationarity. Nonstationarity in head movements was found to be positively related to the number of men in a conversation. Surrogate data analysis offsetting the conversants’ time series by a large lag was unable to reject the null hypothesis that the observed high peak correlations were unrelated to short-term coordination between conversants. One way that high peak correlations could be observed when 2 time series are offset by a large time lag is for each time series to exhibit self-similarity over a range of scales. Multifractal analysis found small-scale fluctuations to be persistent, τ(q) 0.5. These results are consistent with a view that symmetry is formed between conversants over short intervals and that this symmetry is broken at longer, irregular intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
66.
Calear Alison L.; Christensen Helen; Mackinnon Andrew; Griffiths Kathleen M.; O’Kearney Richard 《Canadian Metallurgical Quarterly》2009,77(6):1021
The aim in the current study was to investigate the effectiveness of an online, self-directed cognitive–behavioral therapy program (MoodGYM) in preventing and reducing the symptoms of anxiety and depression in an adolescent school-based population. A cluster randomized controlled trial was conducted with 30 schools (N = 1,477) from across Australia, with each school randomly allocated to the intervention or wait-list control condition. At postintervention and 6-month follow-up, participants in the intervention condition had significantly lower levels of anxiety than did participants in the wait-list control condition (Cohen’s d = 0.15–0.25). The effects of the MoodGYM program on depressive symptoms were less strong, with only male participants in the intervention condition exhibiting significant reductions in depressive symptoms at postintervention and 6-month follow-up (Cohen’s d = 0.27–0.43). Although small to moderate, the effects obtained in the current study provide support for the utility of universal prevention programs in schools. The effectiveness of booster sessions should be explored in future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
67.
Stephen W. Rothwell Evelyn Sawyer Jennifer Dorsey William S. Flournoy Timothy Settle David Simpson Gary Cadd Paul Janmey Charles White Kathleen A. Szabo 《Journal of materials science. Materials in medicine》2009,20(10):2155-2166
We investigated the inflammatory response in pigs exposed to salmon fibrinogen/thrombin dressings. Animals were exposed to
the material in 3 ways: (a) thrombin and fibrinogen were injected intravenously, (b) dual full-thickness skin lesions were
surgically created on the dorsal aspect of the swine and treated with the fibrinogen/thrombin bandage and a commercial bandage
or (c) a fibrinogen/thrombin bandage was inserted through an abdominal incision into the peritoneal cavity. Blood was collected
twice weekly and animals were sacrificed at 7, 10 or 28 days. Animals in the 28-day dermal lesion group were given an injection
of salmon fibrinogen/thrombin at the 10 day point to simulate a second bandage application. The immune response manifested
itself as induction of germinal centers in mesenteric lymph nodes and in the white pulp of the spleen. Examination of the
histology of the skin and organs showed a cellular inflammatory response with granulation tissue and signs of edema that resolved
by the 28-day stage. Antibodies reactive to salmon and human thrombin and fibrinogen were detected, but fibrinogen levels
and coagulation processes were not affected. In conclusion, animals treated with salmon fibrinogen/thrombin bandages demonstrated
a smooth recovery course in terms of both tissue healing and the immune response without adverse effects from the exposure
to the fish proteins. 相似文献
68.
Ankley GT Diamond SA Tietge JE Holcombe GW Jensen KM Defoe DL Peterson R 《Environmental science & technology》2002,36(13):2853-2858
A number of environmental stressors have been hypothesized as responsible for recent increases in limb malformations in several species of North American amphibians. The purpose of this study was to generate dose-response data suitable for assessing the potential role of solar ultraviolet (UV) radiation in causing limb malformations in a species in which this phenomenon seemingly is particularly prevalent, the northern leopard frog (Rana pipiens). Frogs were exposed from early embryonic stages through complete metamorphosis to varying natural sunlight regimes, including unaltered (100%) sunlight, sunlight subjected to neutral density filtration to achieve relative intensities of 85%, 75%, 65%, 50%, and 25% of unaltered sunlight, and sunlight filtered with glass or acrylamide to attenuate, respectively, the UVB (290-320 nm) and UVB plus UVA (290-380 nm) portions of the spectrum. The experiments were conducted in a controlled setting, with continual monitoring of UVB, UVA, and visible light to support a robust exposure assessment. Full sunlight caused approximately 50% mortality of the frogs during early larval development; no significant treatment-related mortality occurred under any of the other exposure regimes, including 100% sunlight with glass or acrylamide filtration. There was a dose-dependent (p < 0.0001) induction of hindlimb malformations in the frogs, with the percentage of affected animals ranging from about 97% under unaltered sunlight to 0% in the 25% neutral density treatment. Malformations were comprised mostly of missing or truncated digits, and generally were bilateral as well as symmetrical. Filtration of sunlight with either glass or acrylamide both significantly reduced the incidence of malformed limbs. The estimated sunlight dose resulting in a 50% limb malformation rate (ED50) was 63.5%. The limb ED50 values based on measured sunlight intensities corresponded to average daily doses of 4.5 and 100 Wh x m(-2) for UVB and UVA, respectively. Exposure to sunlight also resulted in increased eye malformations in R. pipiens, however, the dose-response relationship for this endpoint was not monotonic. The results of this study, in conjunction with measured or predicted exposure data from natural settings, provide a basis for quantitative prediction of the risk of solar UV radiation to amphibians. 相似文献
69.
The solid-phase microextraction (SPME) technique has been used historically to quantify analytes present at the parts per million level. However, the nonintrusive nature of SPME lends itself to other applications involving analytes at higher concentration. In the current work, the possibility of using the SPME technique to measure concentrated gaseous samples was examined. Pentane concentrations between 0 and 100% saturation were studied, over a temperature range of 20-45 degrees C. The results showed that, up to a critical mole fraction in the solid phase, the concentrations of pentane in the polymeric extracting solid and vapor phases were related by a constant, equal to Henry's constant. The temperature dependence of Henry's constant was shown to follow the predicted trend with temperature, as determined from rigorous thermodynamic calculations. Above the pentane concentration in the polymeric phase, the response deviated from linearity. The nonideality was captured in an activity coefficient. An activity coefficient model developed to describe the nonideality was found to be a function of the swollen volume of the SPME polymer phase. The results indicate that the SPME technique can be applied to high analyte concentrations, although difficulties may be encountered when multiple analytes are absorbed. 相似文献
70.
We tested the hypothesis that sex differences in preference for NaCl are attributable to estrogen-mediated alterations in gustatory processing. Electrophysiological responses of the chorda tympani nerve to NaCl were blunted by estrogen treatment in ovariectomized female rats, suggesting that females are less sensitive to concentrated NaCl solutions during high estrogen conditions. In contrast, after a taste aversion was conditioned to 150-mM NaCl, estrogen- and oil-treated ovariectomized rats generalized the aversion to a lower concentration of NaCl than did males, suggesting that females are more sensitive to the taste of dilute NaCl solutions regardless of estrogen. Thus, sex differences in NaCl preferences may be attributable to differences in NaCl taste processing that involve both acute and developmental effects of estrogen. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献