全文获取类型
收费全文 | 109638篇 |
免费 | 7498篇 |
国内免费 | 4350篇 |
专业分类
电工技术 | 5865篇 |
技术理论 | 3篇 |
综合类 | 6069篇 |
化学工业 | 14723篇 |
金属工艺 | 4254篇 |
机械仪表 | 5470篇 |
建筑科学 | 6119篇 |
矿业工程 | 2164篇 |
能源动力 | 2446篇 |
轻工业 | 6547篇 |
水利工程 | 2017篇 |
石油天然气 | 3058篇 |
武器工业 | 927篇 |
无线电 | 9896篇 |
一般工业技术 | 11113篇 |
冶金工业 | 24106篇 |
原子能技术 | 1118篇 |
自动化技术 | 15591篇 |
出版年
2024年 | 296篇 |
2023年 | 1034篇 |
2022年 | 1757篇 |
2021年 | 2500篇 |
2020年 | 1896篇 |
2019年 | 1613篇 |
2018年 | 2141篇 |
2017年 | 2650篇 |
2016年 | 2857篇 |
2015年 | 3519篇 |
2014年 | 3724篇 |
2013年 | 4559篇 |
2012年 | 6719篇 |
2011年 | 7313篇 |
2010年 | 5281篇 |
2009年 | 5244篇 |
2008年 | 5066篇 |
2007年 | 4860篇 |
2006年 | 4667篇 |
2005年 | 6839篇 |
2004年 | 5106篇 |
2003年 | 4373篇 |
2002年 | 3200篇 |
2001年 | 2815篇 |
2000年 | 2061篇 |
1999年 | 2087篇 |
1998年 | 7222篇 |
1997年 | 4708篇 |
1996年 | 3321篇 |
1995年 | 2157篇 |
1994年 | 1595篇 |
1993年 | 1524篇 |
1992年 | 601篇 |
1991年 | 559篇 |
1990年 | 522篇 |
1989年 | 447篇 |
1988年 | 426篇 |
1987年 | 285篇 |
1986年 | 270篇 |
1985年 | 230篇 |
1984年 | 92篇 |
1983年 | 93篇 |
1982年 | 153篇 |
1981年 | 198篇 |
1980年 | 207篇 |
1979年 | 69篇 |
1978年 | 102篇 |
1977年 | 612篇 |
1976年 | 1326篇 |
1975年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
11.
AbstractBreast cancer is a common malignancy with poor prognosis. Cancer cells are heterogeneous and cancer stem cells (CSCs) are primarily responsible for tumor relapse, treatment-resistance and metastasis, so for breast cancer stem cells (BCSCs). Diets are known to be associated with carcinogenesis. Food-derived polyphenols are able to attenuate the formation and virulence of BCSCs, implying that these compounds and their analogs might be promising agents for preventing breast cancer. In the present review, we summarized the origin and surface markers of BCSCs and possible mechanisms responsible for the inhibitory effects of polyphenols on BCSCs. The suppressive effects of common dietary polyphenols against BCSCs, such as curcumin, epigallocatechin gallate (EGCG) and related polyphenolic compounds were further discussed. 相似文献
12.
13.
Traditionally, in supervised machine learning, (a significant) part of the available data (usually 50%-80%) is used for training and the rest—for validation. In many problems, however, the data are highly imbalanced in regard to different classes or does not have good coverage of the feasible data space which, in turn, creates problems in validation and usage phase. In this paper, we propose a technique for synthesizing feasible and likely data to help balance the classes as well as to boost the performance in terms of confusion matrix as well as overall. The idea, in a nutshell, is to synthesize data samples in close vicinity to the actual data samples specifically for the less represented (minority) classes. This has also implications to the so-called fairness of machine learning. In this paper, we propose a specific method for synthesizing data in a way to balance the classes and boost the performance, especially of the minority classes. It is generic and can be applied to different base algorithms, for example, support vector machines, k-nearest neighbour classifiers deep neural, rule-based classifiers, decision trees, and so forth. The results demonstrated that (a) a significantly more balanced (and fair) classification results can be achieved and (b) that the overall performance as well as the performance per class measured by confusion matrix can be boosted. In addition, this approach can be very valuable for the cases when the number of actual available labelled data is small which itself is one of the problems of the contemporary machine learning. 相似文献
14.
15.
16.
Wojciech Jó?wicki Anna A. Bro?yna Jerzy Siekiera Andrzej T. Slominski 《International journal of molecular sciences》2015,16(2):3783-3803
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape. 相似文献
17.
18.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献
19.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
20.