全文获取类型
收费全文 | 425篇 |
免费 | 3篇 |
专业分类
综合类 | 2篇 |
化学工业 | 13篇 |
金属工艺 | 5篇 |
机械仪表 | 5篇 |
建筑科学 | 3篇 |
能源动力 | 2篇 |
轻工业 | 13篇 |
石油天然气 | 3篇 |
无线电 | 7篇 |
一般工业技术 | 13篇 |
冶金工业 | 348篇 |
原子能技术 | 7篇 |
自动化技术 | 7篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 12篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2000年 | 2篇 |
1999年 | 9篇 |
1998年 | 106篇 |
1997年 | 57篇 |
1996年 | 42篇 |
1995年 | 34篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 17篇 |
1976年 | 30篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1967年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有428条查询结果,搜索用时 31 毫秒
201.
Four additional neolignans, comprising obovatifol [(2S,3S)-2,3-dihydro-2- (3,4-dihydroxy-5-methoxyphenyl)-7-methoxy-3-methyl-5-trans-propenyl benzofuran], obovaten [2-(3,4-dihydroxy-5-methoxyphenyl)-7-methoxy-3- methyl-5-trans-propenyl benzofuran], perseal C [(2S,3R)-2,3-dihydro-2-(3,4-methylenedioxyphenyl)-5- formyl-3-hydroxymethyl-7-methoxy benzofuran] and perseal D [2-(3,4-dihydroxy-5-methoxyphenyl)-5-formyl-7- methoxy-3-methyl benzofuran] were isolated in a continuing study of the leaves of Persea obovatifolia. Obovatifol had been reported previously in a mass spectrometric analysis without any other spectroscopic data. Obovaten and perseals C and D are new compounds, bearing a C-1' formyl side-chain, instead of a propenyl group. Their structures were elucidated from spectroscopic data; they showed significant cytotoxic activities against P-388, KB16, A549 and HT-29 cancer cell lines in vitro. 相似文献
202.
The evolution of crystallization and porosity changes with firing temperature were studied in ZnO–B2O3–SiO2–MgO glasses. Those
glasses presintered at 610 °C to a low porosity were crystallized in the temperature range of 690–870 °C. The glasses were
crystallized by a surface crystallization mechanism. The porosity increased with the crystallization temperature. In the temperature
range of 710–790 °C, several crystalline phases, such as 3ZnO–B2O3, willemite (2ZnO–SiO2), 5ZnO–2B2O3, and another form of
zinc silicate (2ZnO–SiO2), produced at relatively low temperatures, were produced, while above 800 °C only the 2ZnO–SiO2 phase
co-existed with a glass phase. Only an observed density difference between the glass and the crystallized glass cannot be
attributed to the void formation during the crystallization reaction. Due to the crystallization the composition of the remaining
glass around the crystalline phases is expected to change. The depletion of a certain component in the remaining glass, probably
the SiO2 due to the production of the 2ZnO–SiO2 phase, might result in the increase in the vapour pressure of the remaining
glass and lead to the observed increase in porosity. Below 800 °C, at which temperature the crystallization rate is fast and
only a small amount of the glass phase remained, the porosity remained constant after the completion of the crystallization.
Contrarily at 860 °C the porosity continuously increased with firing time.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
203.
SC Nicholson JN Robinson IL Sargent DH Barlow 《Canadian Metallurgical Quarterly》1997,68(6):1114-1119
OBJECTIVE: To compare flow cytometry with the established indirect immunobead binding test (IBT) for the detection of antisperm antibodies in seminal plasma. DESIGN: A prospective, comparative study. SETTING: University-based andrology unit. PATIENT(S): One hundred and fifty-eight men with suspected male factor subfertility. INTERVENTION(S): Seminal plasma samples were incubated with antisperm antibody-negative donor sperm. Surface-bound antibody was detected with fluorescence-labeled antihuman antibody in the flow cytometry assay or with immunobead-labeled antihuman antibody in the IBT. MAIN OUTCOME MEASURE(S): The percentage of sperm that tested positive for surface-bound antibody was determined in the two assays. Seminal plasma was antisperm antibody-positive when > or = 20% of the sperm were antibody-bound, and clinically significant levels were present when > or = 50% of the sperm were antibody-bound. RESULT(S): Of 71 samples that were negative by the IMT, 66 (93%) also were negative by flow cytometry. Of 63 samples that had > or = 50% immunobead binding, 55 had equivalent results by flow cytometry. Overall statistical analysis showed a good correlation between the two assays. CONCLUSION(S): There is a good correlation between the indirect IBT and indirect flow cytometry for the detection of antisperm antibodies in seminal plasma. 相似文献
204.
WE Hardman IL Cameron WH Beer KV Speeg SC Kadakia KA Lang 《Canadian Metallurgical Quarterly》1997,6(8):633-637
Data from rat experimental carcinogenesis studies indicate that supplemental dietary cellulose reduces the incidence of colon cancer. Epidemiology studies also indicate that high dietary fiber reduces the risk of colorectal cancer in humans. Patients diagnosed with sporadic adenomas were entered into a randomized clinical trial to determine if supplemental dietary cellulose would reduce the patients' risk for colon cancer. Immunohistochemical staining for transforming growth factor alpha (TGF-alpha) was done on biopsies of rectal mucosa taken from patients at the time of initial polypectomy and 1 year later. Results were evaluated for utility as a surrogate end point biomarker for reduction in colon cancer risk. There was a significant decrease in the fraction of the rectal crypt cells that stained for TGF-alpha in six of seven of the patients given the cellulose supplements but in only one of six of the patients not given cellulose. Thus, whether evaluated as a group or in individual patients, there was a significant decrease in TGF-alpha in rectal crypts due to cellulose intervention, which correlated with the expected ability of supplemental dietary cellulose to decrease the risk for colon cancer. Long-term testing of the ability of dietary cellulose to reduce adenoma recurrence is under way to validate the use of TGF-alpha as a surrogate end point biomarker. 相似文献
205.
206.
Changes in apparent 31P spin-lattice relaxation times (T1) associated with brain development were investigated in rat pups. While analysis of variance showed strong age dependency in [PME]/[ATP] and [PCr]/[ATP], the T1 values of PME, PCr, and ATP did not show any age dependency. The studies indicate that in contrast to the data which indicated aging-related changes in the T1 values of PME, the observed changes in PME during neonatal development are likely to be quantitative in nature. 相似文献
207.
208.
JH Waite IL Neilson 《Canadian Metallurgical Quarterly》1995,11(1):60; discussion 59, 61-60; discussion 59, 62
209.
Crystals of an ion-channel-forming peptaibol peptide in a partial membrane environment have been obtained by cocrystallizing antiamoebin with n-octanol. The antiamoebin molecule has a bent helical conformation very similar to that established for Leu-zervamicin, despite a significantly different sequence for residues 1-8. The bent helices assemble to form a polar channel in the shape of an hour glass that is quite comparable to that of Leu-zervamicin. The molecules of cocrystallized octanol are found in two different areas with respect to the assembly of peptide molecules. One octanol molecule mimics a membrane segment along the hydrophobic exterior of the channel assembly. The other octanol molecules fill the channel in such a way that their OH termini satisfy the C==O moieties directed into the interior of the channel. Structure parameters for C82 H27 N17 O20(.3) C8H18O are space group P2(1) 2(1) 2(1), a = 9.143(2) A, b = 28.590(8) A, c = 44.289(8) A, Z = 4, agreement factor R1 = 11.95% for 4,113 observed reflections [>4sigma(F)], resolution approximately 1.0 A. 相似文献
210.
During fetal lymph node organogenesis in mice, lymph node postcapillary high endothelial venules briefly express the Peyer's patch addressin MAdCAM-1. This allows initial seeding by two unusual lymphocyte populations selectively expressing the Peyer's patch homing receptor integrin alpha4beta 7: CD4+CD3- oligolineage progenitors and TCR gammadelta+ T cells. It was found that the CD4+CD3- cells are lineage-restricted progenitors that express surface lymphotoxin-beta (LTbeta) and the chemokine receptor BLR1. They can differentiate into natural killer cells, dendritic antigen-presenting cells, and follicular cells of unknown outcome, but these cells do not become T or B lymphocytes. In addition to LN, CD4+CD3- cells can also be found in fetal spleen starting at 13.5 dpc, while absent from fetal liver. In view of the necessity of lymphotoxin in lymphoid organ development, it is thought that the novel subset of CD4+CD3- LTbeta+ fetal cells is instrumental in the development of lymphoid tissue architecture. 相似文献