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   1142篇
  免费   100篇
  国内免费   2篇
电工技术   16篇
化学工业   340篇
金属工艺   23篇
机械仪表   38篇
建筑科学   28篇
矿业工程   1篇
能源动力   61篇
轻工业   138篇
水利工程   8篇
石油天然气   3篇
无线电   93篇
一般工业技术   211篇
冶金工业   33篇
原子能技术   4篇
自动化技术   247篇
  2024年   1篇
  2023年   18篇
  2022年   77篇
  2021年   77篇
  2020年   36篇
  2019年   64篇
  2018年   52篇
  2017年   54篇
  2016年   58篇
  2015年   49篇
  2014年   43篇
  2013年   76篇
  2012年   90篇
  2011年   100篇
  2010年   73篇
  2009年   72篇
  2008年   60篇
  2007年   63篇
  2006年   24篇
  2005年   27篇
  2004年   27篇
  2003年   13篇
  2002年   13篇
  2001年   8篇
  2000年   2篇
  1999年   8篇
  1998年   9篇
  1997年   6篇
  1996年   8篇
  1995年   4篇
  1994年   2篇
  1993年   3篇
  1992年   4篇
  1990年   2篇
  1988年   1篇
  1987年   4篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1982年   3篇
  1981年   3篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1957年   1篇
排序方式: 共有1244条查询结果,搜索用时 15 毫秒
991.
Scientometrics - Encouraged by the emergence of a new and growing literature on the use of trademark data as complementary indicators of innovation, this paper strengthens the case for such use by...  相似文献   
992.
993.
Objective

Evaluating the impact of the Inversion Time (TI) on regional perfusion estimation in a pediatric cohort using Arterial Spin Labeling (ASL).

Materials and methods

Pulsed ASL (PASL) was acquired at 3 T both at TI 1500 ms and 2020 ms from twelve MRI-negative patients (age range 9–17 years). A volume of interest (VOIs) and a voxel-wise approach were employed to evaluate subject-specific TI-dependent Cerebral Blood Flow (CBF) differences, and grey matter CBF Z-score differences. A visual evaluation was also performed.

Results

CBF was higher for TI 1500 ms in the proximal territories of the arteries (PTAs) (e.g. insular cortex and basal ganglia — P < 0.01 and P < 0.05 from the VOI analysis, respectively), and for TI 2020 ms in the distal territories of the arteries (DTAs), including the watershed areas (e.g. posterior parietal and occipital cortex — P < 0.001 and P < 0.01 from the VOI analysis, respectively). Similar differences were also evident when analyzing patient-specific CBF Z-scores and at a visual inspection.

Conclusions

TI influences ASL perfusion estimates with a region-dependent effect. The presence of intraluminal arterial signal in PTAs and the longer arterial transit time in the DTAs (including watershed areas) may account for the TI-dependent differences. Watershed areas exhibiting a lower perfusion signal at short TIs (~ 1500 ms) should not be misinterpreted as focal hypoperfused areas.

  相似文献   
994.
Consider an interorganizational open innovation project, in which different organizations cooperate to generate value for clients or to solve a technological problem. In this setting, both the focal firm and the partners face uncertainties over time (e.g., technological uncertainties, market uncertainties) and, therefore, the performance of the focal firm and the overall interorganizational project depend on that firm's ability to assess potential uncertainties. The process of diffusion of a particular uncertainty throughout an inter-organizational project can be defined as uncertainty propagation. Assessment of uncertainty propagation can be employed to mitigate its detrimental impact. This paper connects previous studies of open innovation, uncertainty management and project management by providing a comprehensive, but structured, framework to assess uncertainty propagation. First, we propose the underlying causes of uncertainty propagation. Then, we present the three different approaches to its assessment, based on causes, effects and protection.  相似文献   
995.
Proinflammatory cytokines are produced in pregnancy in response to the invading pathogens and/or nonmicrobial causes such as damage-associated molecules and embryonic semi-allogenic antigens. While inflammation is essential for a successful pregnancy, an excessive inflammatory response is implicated in several pathologies including pre-eclampsia (PE). This review focuses on the proinflammatory cytokine macrophage migration inhibitory factor (MIF), a critical regulator of the innate immune response and a major player of processes allowing normal placental development. PE is a severe pregnancy-related syndrome characterized by exaggerated inflammatory response and generalized endothelial damage. In some cases, usually of early onset, it originates from a maldevelopment of the placenta, and is associated with intrauterine growth restriction (IUGR) (placental PE). In other cases, usually of late onset, pre-pregnancy maternal diseases represent risk factors for the development of the disease (maternal PE). Available data suggest that low MIF production in early pregnancy could contribute to the abnormal placentation. The resulting placental hypoxia in later pregnancy could produce high release of MIF in maternal serum typical of placental PE. More studies are needed to understand the role of MIF, if any, in maternal PE.  相似文献   
996.
The Philadelphia-negative myeloproliferative neoplasms (MPNs) are malignancies of the hematopoietic stem cell (HSC) arising as a consequence of clonal proliferation driven by somatically acquired driver mutations in discrete genes (JAK2, CALR, MPL). In recent years, along with the advances in molecular characterization, the role of immune dysregulation has been achieving increasing relevance in the pathogenesis and evolution of MPNs. In particular, a growing number of studies have shown that MPNs are often associated with detrimental cytokine milieu, expansion of the monocyte/macrophage compartment and myeloid-derived suppressor cells, as well as altered functions of T cells, dendritic cells and NK cells. Moreover, akin to solid tumors and other hematological malignancies, MPNs are able to evade T cell immune surveillance by engaging the PD-1/PD-L1 axis, whose pharmacological blockade with checkpoint inhibitors can successfully restore effective antitumor responses. A further interesting cue is provided by the recent discovery of the high immunogenic potential of JAK2V617F and CALR exon 9 mutations, that could be harnessed as intriguing targets for innovative adoptive immunotherapies. This review focuses on the recent insights in the immunological dysfunctions contributing to the pathogenesis of MPNs and outlines the potential impact of related immunotherapeutic approaches.  相似文献   
997.
The small Ras-related GTPase Rab-28 is highly expressed in photoreceptor cells, where it possibly participates in membrane trafficking. To date, six alterations in the RAB28 gene have been associated with autosomal recessive cone-rod dystrophies. Confirmed variants include splicing variants, missense and nonsense mutations. Here, we present a thorough phenotypical and genotypical characterization of five individuals belonging to four Italian families, constituting the largest cohort of RAB28 patients reported in literature to date. All probands displayed similar clinical phenotype consisting of photophobia, decreased visual acuity, central outer retinal thinning, and impaired color vision. By sequencing the four probands, we identified: a novel homozygous splicing variant; two novel nonsense variants in homozygosis; a novel missense variant in compound heterozygous state with a previously reported nonsense variant. Exhaustive molecular dynamics simulations of the missense variant p.(Thr26Asn) in both its active and inactive states revealed an allosteric structural mechanism that impairs the binding of Mg2+, thus decreasing the affinity for GTP. The impaired GTP-GDP exchange ultimately locks Rab-28 in a GDP-bound inactive state. The loss-of-function mutation p.(Thr26Asn) was present in a compound heterozygosis with the nonsense variant p.(Arg137*), which does not cause mRNA-mediated decay, but is rather likely degraded due to its incomplete folding. The frameshift p.(Thr26Valfs4*) and nonsense p.(Leu13*) and p.(Trp107*) variants, if translated, would lack several key structural components necessary for the correct functioning of the encoded protein.  相似文献   
998.
999.
In this study, seed productivity and oil content of three safflower genotypes (IMAMT 1750, IMAMT 946 and IMAMT 894) cultivated in the Brazilian semi-arid region were evaluated to identify which genotype has the best in-field performance. The acidity and saponification index were evaluated, as well as the efficiency of lipid extraction through thermal analysis, aiming to estimate the species' potential for biofuel production in semi-arid regions. Field cultivation under semi-arid conditions lasted for ~75 days and no herbivory were observed on the plants. The IMAMT 894 genotype presented higher seed yield than the other genotypes, IMAMT 1750 presented 34% oil, and IMAMT 946 and IMAMT 894 presented 32% oil with efficient extraction in the Soxhlet system and high oil content and quality; higher than traditionally used crops such as soybean and cotton. The IMAMT 894 genotype showed higher seed productivity, but all three genotypes presented good oil yield and quality for biodiesel production. Oil extraction in the Soxhlet system was efficient since the thermogravimetric analysis showed no oil in the residual biomass after oil extraction.  相似文献   
1000.
Glassy carbon (GC) constitutes a promising carbonaceous material that can be employed as an antistatic agent in the development of antistatic packaging used in the electronics industry. Thus, the present work aims at developing biodegradable and antistatic packaging from poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) reinforced with different GC contents (0, 0.5, 1.0, 2.5, and 5.0 wt%) and different GC particle size (<45 μm and > 75 μm) using extrusion processing. differential scanning calorimetry analysis shows that the addition of GC decreases the degree of crystallinity (Xc) of PHBV, which can explain the reduction of its stiffness. Impedance spectroscopy results reveal that the use of GC contents greater than 2.5 wt% (GC > 75 μm) makes possible the obtainment of a material with an electrical resistivity small enough to be used in antistatic packaging. It can be concluded that GC is an interesting alternative of antistatic agent for electrically dissipative packaging.  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