全文获取类型
收费全文 | 21791篇 |
免费 | 2182篇 |
国内免费 | 7篇 |
出版年
2022年 | 116篇 |
2021年 | 246篇 |
2020年 | 171篇 |
2019年 | 215篇 |
2018年 | 239篇 |
2017年 | 235篇 |
2016年 | 449篇 |
2015年 | 722篇 |
2014年 | 816篇 |
2013年 | 984篇 |
2012年 | 1411篇 |
2011年 | 1451篇 |
2010年 | 921篇 |
2009年 | 857篇 |
2008年 | 1138篇 |
2007年 | 1256篇 |
2006年 | 1079篇 |
2005年 | 1101篇 |
2004年 | 1126篇 |
2003年 | 1076篇 |
2002年 | 1043篇 |
2001年 | 360篇 |
2000年 | 332篇 |
1999年 | 371篇 |
1998年 | 340篇 |
1997年 | 237篇 |
1996年 | 248篇 |
1995年 | 236篇 |
1994年 | 225篇 |
1993年 | 222篇 |
1992年 | 289篇 |
1991年 | 232篇 |
1990年 | 249篇 |
1989年 | 265篇 |
1988年 | 238篇 |
1987年 | 217篇 |
1986年 | 190篇 |
1985年 | 209篇 |
1984年 | 243篇 |
1983年 | 183篇 |
1982年 | 198篇 |
1981年 | 189篇 |
1980年 | 175篇 |
1979年 | 164篇 |
1978年 | 154篇 |
1977年 | 127篇 |
1976年 | 135篇 |
1975年 | 116篇 |
1974年 | 137篇 |
1973年 | 119篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Based on its proven anabolic effects on bone in osteoporosis patients, recombinant parathyroid hormone (PTH1-34) has been evaluated as a potential therapy for skeletal repair. In animals, the effect of PTH1-34 has been investigated in various skeletal repair models such as fractures, allografting, spinal arthrodesis and distraction
osteogenesis. These studies have demonstrated that intermittent PTH1-34 treatment enhances and accelerates the skeletal repair process via a number of mechanisms, which include effects on mesenchymal
stem cells, angiogenesis, chondrogenesis, bone formation and resorption. Furthermore, PTH1-34 has been shown to enhance bone repair in challenged animal models of aging, inflammatory arthritis and glucocorticoid-induced
bone loss. This pre-clinical success has led to off-label clinical use and a number of case reports documenting PTH1-34 treatment of delayed-unions and non-unions have been published. Although a recently completed phase 2 clinical trial of PTH1-34 treatment of patients with radius fracture has failed to achieve its primary outcome, largely because of effective healing
in the placebo group, several secondary outcomes are statistically significant, highlighting important issues concerning the
appropriate patient population for PTH1-34 therapy in skeletal repair. Here, we review our current knowledge of the effects of PTH1-34 therapy for bone healing, enumerate several critical unresolved issues (e.g., appropriate dosing regimen and indications)
and discuss the long-term potential of this drug as an adjuvant for endogenous tissue engineering. 相似文献
2.
3.
The influence of the protein matrix on the reactivity of external molecules with a species buried within the protein interior is considered in two general ways: (1) there may be structural fluctuations that allow for the diffusive penetration of the small molecules and/or (2) the external molecule may react over a distance. As a means to study the protein matrix, a reactive species within the protein can be formed by exciting tryptophan to the triplet state, and then the reaction of the triplet-state molecule with an external molecule can be monitored by a decrease in phosphorescence. In this work, the quenching ability (i.e., reactivity) was examined for H2S, CS2, and NO2- acting on tryptophan phosphorescence in parvalbumin, azurin, horse liver alcohol dehydrogenase, and alkaline phosphatase. A comparison of charged versus uncharged quenchers (H2S vs SH- and CS2 vs NO2-) reveals that the uncharged molecules are much more effective than charged species in quenching the phosphorescence of fully buried tryptophan, whereas the quenching for exposed tryptophan is relatively independent of the charge of the quencher. This is consistent with the view that uncharged triatomic molecules can penetrate the protein matrix to some extent. The energies of activation of the quenching reaction are low for the charged quenchers and higher for the uncharged CS2. A model is presented in which the quenchability of a buried tryptophan is inversely related to the distance from the surface when diffusion through the protein is the rate-limiting step.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
4.
5.
6.
A F Wright 《BMJ (Clinical research ed.)》1982,285(6342):609-611
7.
Shira Weingarten-Gabbay Susan Klaeger Siranush Sarkizova Leah R. Pearlman Da-Yuan Chen Kathleen M.E. Gallagher Matthew R. Bauer Hannah B. Taylor W. Augustine Dunn Christina Tarr John Sidney Suzanna Rachimi Hasahn L. Conway Katelin Katsis Yuntong Wang Del Leistritz-Edwards Melissa R. Durkin Christopher H. Tomkins-Tinch Pardis C. Sabeti 《Cell》2021,184(15):3962-3980.e17
- Download : Download high-res image (225KB)
- Download : Download full-size image
8.
Bruce R. Dorrbecker Susan H. Mercik Paul A. Kramer 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1984,336(1)
A high-performance liquid chromatographic procedure is reported for reproducibly and sensitively quantitating caffeine and its N-demethylated metabolite paraxanthine in micro-samples. A 5-μm reversed-phase radial compression column and 214-nm fixed wavelength ultraviolet detector were used to attain a sensitivity sufficient to quantitate these compounds at concentratios as low as 80 ng/ml using only 25 μl of sample. The assay is applicable to microliter samples of whole blood, serum, plasma, saliva, amniotic, cerebro-spinal and gastric fluids such as might be obtained in studies involving small animals or neonates. The utility of the assay is illustrated with caffeine and paraxanthine levels measured in several maternal and fetal fluids following constant-rate intravenous infusion of caffeine into a rabbit throughout pregnancy. 相似文献
9.
10.
Rebecca R. Sharitz Susan A. Wineriter Michael H. Smith Edwin H. Liu 《American journal of botany》1980,67(9):1297-1303
Biochemical phenotsypes of four taxa of Typha from the eastern United States were determined by starch gel electrophoresis. The isozyme banding patterns of T. latifolia, T. angustifolia and T. domingensis are distinct and allow unambiguous species identification when morphological characters are inadequate or unsuitable. The fourth form, T. glauca, is not an F1 hybrid, but it does appear to be intermediate between T. latifolia and T. angustifolia. The status of T. glauca and evolutionary relationships among the four forms may now be clarified by additional sampling because of the distinct and relatively invariant isozyme banding patterns which are described. 相似文献