全文获取类型
收费全文 | 908篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
化学工业 | 4篇 |
金属工艺 | 2篇 |
建筑科学 | 2篇 |
矿业工程 | 1篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
一般工业技术 | 3篇 |
冶金工业 | 893篇 |
自动化技术 | 3篇 |
出版年
2023年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2017年 | 1篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2011年 | 1篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2000年 | 1篇 |
1999年 | 27篇 |
1998年 | 282篇 |
1997年 | 161篇 |
1996年 | 109篇 |
1995年 | 71篇 |
1994年 | 45篇 |
1993年 | 53篇 |
1992年 | 8篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 19篇 |
1976年 | 21篇 |
1975年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有910条查询结果,搜索用时 15 毫秒
771.
PURPOSE: Ultrasound (US)-guided permanent prostate implants typically use US prostate volumes to plan the implant procedure and CT prostate volumes for 3D dosimetric evaluation of the implant. Such a protocol requires that CT and US prostate volumes be registered. We have studied the impact of prostate volume registration on postimplant dosimetry for patients with low-grade prostate cancer treated with combined US and fluoroscopic-guided permanent implants. METHODS AND MATERIALS: A US image set was obtained with the patient in the lithotomy position to delineate the prostate volume that was subsequently used for treatment planning. Each plan was customized and optimized to ensure complete coverage of the US prostate volume. After implant, a CT scan was obtained for postimplant dosimetry with the patient lying supine. Sources were localized on CT by interactively creating orthogonal images of small cubes, whose dimensions were slightly larger than the source, to assure unique identification of each seed. Ultrasound and CT 3D surfaces were registered using either (a) the rectal surface and base of the prostate, or (b) the Foley balloon and urethra as the alignment reference. A dose distribution was assigned to the US prostate volume based on the CT source distribution, and the dose-volume histogram (DVH) was calculated. RESULT: Prostate volumes drawn from US images differ from those drawn from CT images with the CT volumes being typically larger than the US volumes. Urethral registration of the prostate volume based on aligning the prostatic urethra generates a dose distribution that best follows the preimplant plan and is geometrically the preferable choice for dosimetry. CONCLUSION: The dose distribution and the DVH for the US prostate is sensitive to the mode of registration limiting the ability to determine if acceptable dose coverage has been achieved. 相似文献
772.
773.
Silver-stainable proteins (SSPs) are aspartic acid-rich nuclear proteins which are silver stained under very specific conditions. Using a degenerate oligodeoxyncleotide probe which codes for acidic amino acid residues, a cDNA for a new SSP, referred to as SSP29, has been isolated. The cDNA-derived amino acid sequence shows SSP29 has a molecular mass of 29 kDa, leucine-rich repeats (LRR) near the NH2-terminal region and acidic clusters at the COOH-terminal portion, indicating that SSP29 is also a member of the LRR subfamily of acidic proteins which have been shown to be involved in antigen-mediated cellular responses, leukemogenesis and differentiation. SSP29 can be stained by Ag-NOR staining. SSP29 is expressed in all human tissues and cell lines tested, localized to nucleoplasm and translocated partially to the nucleoli after heat shock. Its interaction with RNA polymerase I suggests that SSP29 may participate in signal transduction that directs nucleolar activities by regulating ribosomal RNA biosynthesis. 相似文献
774.
YA Muller B Li HW Christinger JA Wells BC Cunningham AM de Vos 《Canadian Metallurgical Quarterly》1997,94(14):7192-7197
Vascular endothelial growth factor (VEGF) is a homodimeric member of the cystine knot family of growth factors, with limited sequence homology to platelet-derived growth factor (PDGF) and transforming growth factor beta2 (TGF-beta). We have determined its crystal structure at a resolution of 2.5 A, and identified its kinase domain receptor (KDR) binding site using mutational analysis. Overall, the VEGF monomer resembles that of PDGF, but its N-terminal segment is helical rather than extended. The dimerization mode of VEGF is similar to that of PDGF and very different from that of TGF-beta. Mutational analysis of VEGF reveals that symmetrical binding sites for KDR are located at each pole of the VEGF homodimer. Each site contains two functional "hot spots" composed of binding determinants presented across the subunit interface. The two most important determinants are located within the largest hot spot on a short, three-stranded sheet that is conserved in PDGF and TGF-beta. Functional analysis of the binding epitopes for two receptor-blocking antibodies reveal different binding determinants near each of the KDR binding hot spots. 相似文献
775.
PURPOSE: The purpose of this study was to evaluate the outcome of patients with healed moderate to severe contact lens-associated corneal infectious ulcers who were re-fit with contact lenses. METHODS: We retrospectively studied patients who were fit with contact lenses on our service and who had had moderate to severe corneal infectious ulcers associated with previous contact lens use. Six patients were included in the study. RESULTS: Gas permeable contact lenses were fit in five patients, and a soft contact lens was fit in one patient. Successful fit was achieved in all cases and visual acuities were equal to or better than 20/30 in all patients. No significant complications were observed after a mean follow-up of 23 months (range, 6-45 months). CONCLUSION: In this small series of patients with a history of moderate to severe contact-lens related infectious keratitis, no complications were observed after contact lenses were refit. Contact lens wear in patients with a history of infectious keratitis may be safe and useful in order to achieve visual rehabilitation. 相似文献
776.
This paper examines multifaceted aspects of diving entries into water which are the cause of many critical injuries (costed at $A150 million) and therefore have important safety ramifications. Wedge and compression fractures are most commonly found in the cervical area of the spine with off-centre impacts with the pool or sea bottom. Diving-related injuries range from 2.3 in a South African study to 21% of spinal cord injuries in Poland. Alcohol and diving do not mix because of diminished awareness and information processing. Children aged under 13 years suffer fewer cervical injuries (1 to 4%), but complication rates are relatively high for this group. Sports trauma (diving-related in particular) is one of the more prevalent causes of spinal cord injury in children aged 6 to 15 years. The highest incidence occurs among those aged 10 to 14, followed by the group aged 5 to 9 years. This contradicts the common perception that 15-to 19-year-olds comprise the highest risk group. Boys are more frequently injured, and swimming pools are more common as an injury location then is the case with adults. The role played by water depth has been conclusively ascertained; technique, and therefore education, appear to be more important considerations in injury prevention. Although 89% of injuries occur in water < 1.52m, injuries are rare in water of 0.46 to 0.61m. Care with pool design to avoid sudden depth changes and the resultant "spinal wall' is necessary. Minimum depth values for diving vary from 1 to 1.52 m. Velocities and angles of entry are considered to ascertain the body's decelerative capacity upon entry. The scoop, racing start dive has been shown to require at least 1.22 m of water even when practised by trained divers; the risks involved must therefore be weighed against the fact that it may be no faster than more conventional dives. While it may be safe to perform kneeling and crouching dives into shallowers water, standing dives by untrained divers require a greater margin of error. Lack of education is an issue which needs to be addressed and this paper makes recommendations for safety practices such as steering up to the surface, head protection with the arms and only diving when absolutely necessary. 相似文献
777.
The neisserial fbpABC locus has been proposed to act as an iron-specific ABC transporter system. To confirm this assigned function, we constructed an fbpABC mutant in Neisseria meningitidis by insertional inactivation of fbpABC with a selectable antibiotic marker. The mutant was unable to use iron supplied from human transferrin, human lactoferrin, or iron chelates. However, the use of iron from heme and human hemoglobin was unimpaired. These results support the obligatory participation of fbpABC in neisserial periplasmic iron transport and do not indicate a role for this genetic locus in the heme iron pathway. 相似文献
778.
We report five cases of reactive mediastinal spindle cell proliferations associated with anthracosis and anthracosilicosis that simulated a malignant process both on clinical and morphological grounds. Clinically, the lesions formed radiographically evident masses or were infiltrative. Microscopically, a prominent storiform pattern of intertwining spindle cells was found in four cases. This proliferation extended outside of the lymph node capsule in three cases and surrounded nerves in two. Because of this combination of features, the submitted diagnoses included a malignant neoplasm in four cases. The spindle cells were immunoreactive for histiocytic markers and focally contained fine anthracotic pigment. All cases featured nodular hyaline scars and contained polarizable material suggestive of silica, although a history of industrial exposure was obtained in only two cases. No lesion has enlarged or otherwise progressed during follow-up ranging from 6 to 48 months. The differential diagnosis includes a variety of spindle cell neoplasms, including malignant fibrous histiocytoma, follicular dendritic cell tumor, spindle cell melanoma, and Kaposi's sarcoma. 相似文献
779.
KT Hopkins WD Wilson BC Bender DR McCurdy JE Hall RR Tidwell A Kumar M Bajic DW Boykin 《Canadian Metallurgical Quarterly》1998,41(20):3872-3878
The syntheses of nine new derivatives of 2, 5-bis[4-(N-alkylamidino)phenyl]furans with extended aromatic systems are reported. The interaction of these dicationic furans with poly(dA)poly(dT) and with the duplex oligomers d(CGCGAATTCGCG)2 and d(GCGAATTCGC)2 was determined by Tm measurement, and the effectiveness of these compounds against the immunosuppressed rat model of Pneumocystis carinii was evaluated. At a screening dose of 10 micromol/kg, 4 of the 12 amidino furans described here are more active than the parent compound 1. In general, extension of the aromatic system in the absence of a substitution of the amidino nitrogens resulted in higher affinity for DNA than the parent compound as judged by the larger DeltaTm values and suggests enhanced van der Waals interactions in the amidino furan-DNA complex. Three of the compounds, 3, 5, and 11, yield cysts counts of less than 0.1% of control when administered at a dosage of 10 micromol/kg. Compound 3, which does not have an extended aromatic system, is the most active derivative. Although a direct correlation between anti-P. carinii activity and DNA binding affinity was not observed, all compounds which have significant activity have large DeltaTm values. 相似文献
780.
M Matteis E Troisi BC Monaldo C Caltagirone M Silvestrini 《Canadian Metallurgical Quarterly》1998,29(5):963-967
BACKGROUND AND PURPOSE: Hemodynamic factors seem to play an important role in the pathogenesis of cerebral ischemic events. The aim of this study was to evaluate whether changes in cerebrovascular reactivity occur in women after menopause. METHODS: Using transcranial Doppler ultrasonography, we studied the changes of flow velocity after hypercapnia in the middle cerebral arteries of 45 healthy premenopausal women (mean age, 32.3 years; range, 20 to 47 years) and 40 postmenopausal women (mean age, 54.4 years; range, 48 to 64 years). The same measurements were recorded in two groups of healthy male subjects age matched with premenopausal (45 subjects) and postmenopausal women (40 subjects). Moreover, a subgroup of postmenopausal women aged 48 to 53 years (15 subjects) were compared with a group of 15 premenopausal women of the same age. We obtained hypercapnia with breath holding and evaluated cerebrovascular reactivity with the breath-holding index (BHI). RESULTS: BHI was significantly lower in postmenopausal women (0.89+/-0.3) than in premenopausal women (1.59+/-0.3; P<0.0001) and in young (1.34+/-0.5; P<0.001) and old men (1.20+/-0.4; P<0.04). In the latter group, BHI was significantly lower than in premenopausal women (P<.0001). BHI values were also significantly lower in postmenopausal than in premenopausal women of the same age (0.81+/-0.1 versus 1.34+/-0.1; P<0.0001). CONCLUSIONS: These findings suggest that the large reduction of cerebrovascular reactivity in postmenopausal women cannot be considered a simple factor related to aging but is probably influenced by hormonal changes. The alteration in cerebrovascular regulation could be involved in the increase of cerebrovascular disease in postmenopausal women. 相似文献