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   1188篇
  免费   23篇
  国内免费   4篇
电工技术   84篇
化学工业   271篇
金属工艺   44篇
机械仪表   15篇
建筑科学   23篇
能源动力   58篇
轻工业   116篇
水利工程   3篇
石油天然气   3篇
无线电   83篇
一般工业技术   224篇
冶金工业   169篇
原子能技术   55篇
自动化技术   67篇
  2023年   3篇
  2022年   18篇
  2021年   18篇
  2020年   11篇
  2019年   22篇
  2018年   30篇
  2017年   19篇
  2016年   14篇
  2015年   9篇
  2014年   32篇
  2013年   60篇
  2012年   48篇
  2011年   51篇
  2010年   39篇
  2009年   51篇
  2008年   61篇
  2007年   57篇
  2006年   38篇
  2005年   45篇
  2004年   43篇
  2003年   43篇
  2002年   31篇
  2001年   17篇
  2000年   11篇
  1999年   34篇
  1998年   66篇
  1997年   51篇
  1996年   37篇
  1995年   31篇
  1994年   33篇
  1993年   27篇
  1992年   17篇
  1991年   12篇
  1990年   14篇
  1989年   14篇
  1988年   12篇
  1987年   11篇
  1986年   10篇
  1985年   4篇
  1984年   12篇
  1983年   4篇
  1982年   9篇
  1981年   6篇
  1980年   3篇
  1979年   8篇
  1978年   7篇
  1977年   6篇
  1976年   6篇
  1975年   3篇
  1972年   3篇
排序方式: 共有1215条查询结果,搜索用时 15 毫秒
151.
Formation of an amorphous Al2Si2O5 layer on a steel pipe surface, after granite–dry steam interaction in the presence of copper, has been determined by XRD analysis and SEM (with energy dispersive X-ray microanalysis). Kinetic data indicate high-protective properties of the Al2Si2O5 layer, which formed a three-dimension substrate ∼5 μm thick, after 100 h exposure.  相似文献   
152.
A prospective study of activated protein C sensitivity, protein C, protein S, and other coagulation factors in 239 women during normal pregnancy was carried out. Protein C activity appeared unaffected by gestation, although an elevation of protein C activity was observed in the early puerperium. A fall in total and free protein S with increasing gestation was observed. Activated protein C sensitivity ratio (APC:SR) showed a progressive fall through pregnancy. This fall correlated with changes in factor VIIIc, factor Vc and protein S. 38% of subjects, with no evidence of Factor V Leiden or anticardiolipin antibodies, showed a low APC:SR (APC:SR <2.6) in the third trimester of pregnancy. Aside from a significant reduction in birth weight, no difference in pregnancy outcome was observed between these subjects and those with a normal APC:SR. Activated protein C sensitivity ratio, modified by pre-dilution of patient samples with factor V depleted plasma, showed no consistent trend with gestation.  相似文献   
153.
PURPOSE: To determine the maximum tolerated dose, toxicities, and potential antitumor activity of edatrexate (E), an antifolate agent with enhanced in vitro antitumor activity as compared with methotrexate (M), when given in combination with vinblastine, doxorubicin, cisplatin, and filgrastim (G-CSF) to patients with advanced malignancies. PATIENTS AND METHODS: Thirty-seven patients with advanced malignancies were treated with escalating doses of edatrexate in combination with vinblastine (V), doxorubicin (A), cisplatin (C), and filgrastim (EVAC/G-CSF) following three different subsequently developed schedules. Schedule 1 was patterned after the MVAC regimen, a combination chemotherapy program with activity against different epithelial malignancies, and consisted of E, 40 mg/m2/day, days 1/15/22; V, 3 mg/m2/day, days 2/15/22; A, 30 mg/m2/ day, day 2; C, 70 mg/m2/day, day 2; repeated every 28 days. Schedules 2 and 3 were designed to avoid observed dose-limiting toxicity on schedule 1 consisting of transient elevation of serum creatinine levels and delayed myelosuppression. Schedule 2 consisted of E, 40 or 60 mg/ m2/day, days 1 and 15; V, 3 mg/m2/day, days 2 and 15; A, 30 mg/m2/day, day 2; C, 30 mg/m2/day, days 1 and 2; cycled every 28 days. Schedule 3 consisted of E, 60 to 120 mg/m2/day, day 1; V, 3 mg/m2/day, day 2; A, 30 mg/m2/day, day 2; C, 30 mg/m2/day, days 1 and 2; cycled every 21 days. Filgrastim 5 micrograms/kg/day was given to all patients subcutaneously until the absolute neutrophil count was greater than 10,000/microL postnadir. Three patients were treated on schedule 1, 10 on schedule 2 (four at an E dose of 40 mg/m2/day and six at an E dose of 60 mg/m2/day), and 24 on schedule 3 (six at each of the following E dosages: 60, 80, 100, and 120 mg/m2/day). RESULTS: Dose-limiting toxicities of grade 3 to 4 leukopenia and transient elevation of serum creatinine values were observed in two of three patients treated on schedule 1. A dose-limiting toxicity of grade 3 to 4 leukopenia was noted in two of six patients treated on schedule 2 at an edatrexate dose of 60 mg/m2/day. Two of six patients treated on schedule 3 at an edatrexate dose of 120 mg/m2/day had a dose-limiting toxicity of grade 3 stomatitis (one patient) and grade 3 cytopenia (one patient). Nineteen of 37 patients with evaluable or measurable disease had a response to treatment (response rate 51%, 95% confidence intervals = 35%-67%). Nine of 15 patients with metastatic non-small cell lung cancer responded, including one complete remission (response rate 60%, confidence intervals = 35%-85%). A median survival of 517 days (confidence interval = 163-808 days) and a 1-year survival rate of 60% (confidence interval = 35%-85%) was seen in patients with advanced non-small cell lung cancer. CONCLUSIONS: The maximum tolerated dose and the recommended phase II dose of edatrexate is 100 mg/m2/day when administered as part of the EVAC/G-CSF program following schedule 3. Promising antineoplastic activity against non-small cell lung carcinomas was observed, and a phase II study is planned.  相似文献   
154.
Jha  Madan K.  Chikamori  K.  Kamii  Y.  Yamasaki  Y. 《Water Resources Management》1999,13(6):443-470
The Konan groundwater basin of Kochi Prefecture, Japan, is experiencing freshwater shortages for the past few years, particularly during the winter season. The present study aimed at analyzing the problem and exploring increased groundwater withdrawals to meet burgeoning freshwater demands in various sectors. The trend analysis of waterconsumption indicates that the groundwater demandwould increase by 43 and 52% by the years 2010 and2025, respectively, compared to 32 100 m3 d-1 at present.The streamflow of the Monobe River reduces to a minimumin winter and it shows a decreasing trend in recentyears. The geologic investigation results indicatethat unconfined (phreatic) aquifers comprisingalluvial sand and gravel and/or diluvial silty sandand gravel are dominant, and that the northwestern andwestern portions of the basin have greater potentialfor groundwater. Groundwater flows essentially fromnorth to south into the ocean. Groundwater levelfluctuations over the basin vary appreciably in spaceand time, indicating a wide variation of naturalrecharge. Field observations confirm the hypothesisthat stream-aquifer interaction also significantlycontributes to groundwater recharge, besides therainfall infiltration. Further, the pumping testsresults demonstrate that though the aquifers arelow-yielding, enhanced groundwater withdrawals couldbe possible. The aquifer hydraulic conductivity ischaracterized as high and ranges from 65 to 804 m d-1(mean = 229 m d-1), thereby suggesting great aquiferheterogeneity. Finally, it is concluded that thelong-term sustainability of the scarce groundwaterresource of the Konan basin is doubtful, and that acomprehensive analysis of the groundwater system isessential prior to formulating plans for the futuregroundwater development and management.  相似文献   
155.
The production and evaluation of non-radioactive probes for the detection of 'Candidatus Liberobacter asiaticum' and 'Candidatus Liberobacter africanum', the two bacterial species associated with citrus huanglongbing (greening) disease is described. Two DNA fagments, In 2.6 and AS 1.7, obtained previously from the beta operons of 'Candidatus Liberobacter asiaticum' and 'Candidatus Liberobacter africanum', respectively, were the starting materials for production of the two non-radioactive probes. These digoxigenin (DIG)-labelled probes were generated by PCR incorporation of DIG-11-dUTP, yielding In 1.7-DIG and AS 1.7-DIG. Probe In 1.7-DIG was hybridized with DNAs extracted from 24 field-collected samples in Bali (Indonesia). The membrane on which the DNAs were blotted was first hybridized with radioactive probe 32P-In 2.6. After the hybridization results were recorded, the radioactive probe was removed, and the membrane hybridized with DIG-labelled probe In 1.7-DIG. Identical results were obtained for 23 samples. One sample was positive with the DIG-labelled probe and negative with the 32P-labelled probe. However, cross-hybridization of In 1.7-DIG with DNA from L. africanum was higher than that obtained with the radioactive probe. This cross-hybridization could be eliminated by raising the temperature of the stringent washing step. No field samples from Africa being available, probe AS 1.7-DIG was dot-blot hybridized against DNAs extracted from leaves of greenhouse-kept citrus plants from different geographical origins and infected with one or other Liberobacter species. The data showed that AS 1.7-DIG hybridized with L. africanum with a sensitivity equivalent to that of the radioactive probe.  相似文献   
156.
In this paper we consider nonlinear, infinite networks of purely resistive type where the voltage across a branch of the network is proportional to a fixed power of the current flowing in the branch. It is known that the study of currents in such networks amounts to studying the space of the functions on a network which have finite Dirichlet sums of orderp. Such a study was carried out in [7], [9], and [11]–[14] under the assumption that every node is connected to only finitely many different nodes of the network. In this paper we drop this assumption and work with general countable networks. We prove that most results of the locally finite case, and especially the classification theory, hold true in a more general context. Moreover, we give necessary and sufficient conditions for a network to have only constant Dirichlet finitep-harmonic functions. The relationship with discrete Markov processes is also pointed out.  相似文献   
157.
Various derivatives of recombinant human granulocyte colony-stimulating factor (rhG-CSF) have been overproduced in Escherichia coli with the strong, inducible trp promoter. A derivative designated as KW-2228 in which the amino acids were replaced at five positions showed more potent granulopoietic activity and stability than those of wild-type both in vitro and in vivo. The purification involved a sequential renaturation process and three-step chromatography. Refolding succeeded in very high yield using a urea system. The purity of KW-2228 was greater than 99% as measured by SDS-PAGE and HPLC analysis. According to circular dichroism and nuclear magnetic resonance spectroscopy, rhG-CSF and KW-2228 have very similar conformations. This suggests that the substitution of five amino acids does not appreciably change the conformation of hG-CSF. KW-2228 ([Ala1, Thr3, Tyr4, Arg5, and Ser17]-hG-CSF) and derivative A ([Ala1, Thr3, Tyr4, Arg5]-hG-CSF) are easily crystallized and they show similar in vitro activity. On the other hand, neither rhG-CSF nor derivative B ([Ser17]-hG-CSF) are crystallized under the same conditions. Thus, the four amino acid substitution (Ala1, Thr3, Tyr4, Arg5) of the N-terminal sequence may facilitate crystallization. The change of Cys17 to Ser may not influence the stability and activity of hG-CSF.  相似文献   
158.
159.
Goldfish were classically conditioned to a mixture of two pulse trains differing in both repetition rate and the spectral profile of the pulses. Animals were then tested for generalization to single pulse trains having one or the other spectral profile presented at a variety of repetition rates. Generalization functions of repetition rate were qualitatively similar to those obtained following conditioning to either of the pulse trains alone. Thus, the spectral profile of each pulse type was appropriately associated with the repetition rate at which that pulse type was presented during conditioning. These results indicate that the two concurrent pulse trains making up the conditioning stimuli were analyzed independently, forming two auditory streams. When either of the two pulse trains were presented with a 500 ms onset asynchrony, stream segregation was enhanced. These and other results suggest that many fundamental features of the human sense of hearing are widely shared among vertebrate animals, and may have developed first among fishes.  相似文献   
160.
Plasma-deposited polycrystalline Si films [or microcrystalline Si (μc-Si) films] produced by plasma enhanced chemical vapor deposition (PECVD) have attracted considerable attention as novel, low-cost and stable materials for the photovoltaic i-layer in p–i–n junction thin-film solar cells. The μc-Si films prepared under various deposition conditions show widely various microstructures, from a crystalline–amorphous mixed state to an almost perfect crystalline state, with different crystallographic orientations. These structural changes directly influence the carrier transport properties that play a dominant role in determining photovoltaic performance. Furthermore, obtaining a uniform built-in electric field throughout the i-layer is a crucial issue for achieving excellent photovoltaic performance. To obtain a uniform electric field, the following terms should be required for the i-layer: ‘truly’ intrinsic characteristic (or not n-type characteristics) as well as structural uniformity in the growth direction without an incubation layer. Here, structural properties of μc-Si for achieving truly intrinsic characteristics are reviewed with an emphasis on collations with the crystalline volume function and the degree of (2 2 0) crystallographic preferential orientation in the crystalline phase. In addition, we reviewed a growth mechanism for the μc-Si film that is actually used in the photovoltaic i-layer in highly efficient solar cells: hybrid-phase growth consisting of conventional vapor-phase growth at the surface and the solid-phase crystallization that simultaneously occurs in the film. That growth is very effective in producing structural uniformity along the growth direction and for formation of crystallites directly on the underlying doped layer.  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