全文获取类型
收费全文 | 6724篇 |
免费 | 441篇 |
国内免费 | 1篇 |
专业分类
7166篇 |
出版年
2024年 | 11篇 |
2023年 | 64篇 |
2022年 | 87篇 |
2021年 | 166篇 |
2020年 | 141篇 |
2019年 | 153篇 |
2018年 | 193篇 |
2017年 | 185篇 |
2016年 | 244篇 |
2015年 | 370篇 |
2014年 | 367篇 |
2013年 | 496篇 |
2012年 | 577篇 |
2011年 | 567篇 |
2010年 | 353篇 |
2009年 | 289篇 |
2008年 | 382篇 |
2007年 | 367篇 |
2006年 | 309篇 |
2005年 | 291篇 |
2004年 | 293篇 |
2003年 | 226篇 |
2002年 | 218篇 |
2001年 | 60篇 |
2000年 | 52篇 |
1999年 | 51篇 |
1998年 | 74篇 |
1997年 | 52篇 |
1996年 | 32篇 |
1995年 | 37篇 |
1994年 | 31篇 |
1993年 | 32篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 33篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1973年 | 12篇 |
1968年 | 17篇 |
1964年 | 7篇 |
排序方式: 共有7166条查询结果,搜索用时 15 毫秒
151.
152.
153.
Felipe Couñago Ana Aurora Díaz Gavela Gemma Sancho Irene Ortiz Francisco José Marcos Manuel Recio Julio Fernández Raquel Cano Mar Jiménez Israel J. Thuissard David Sanz-Rosa Juan Castro Nováis Eduardo Pardo Yolanda Molina Hugo Pérez García Elia del Cerro 《Reports of Practical Oncology and Radiotherapy》2019,24(5):472-480
AimTo analyse the efficacy and toxicity of postprostatectomy SRT in patients with a BCR evaluated with mpMRI.BackgroundMultiparametric magnetic resonance imaging (mpMRI) has the ability to detect the site of pelvic recurrence in patients with biochemical recurrence (BCR) after radical prostatectomy (RP). However, we do not know the oncological outcomes of mpMRI-guided savage radiotherapy (SRT).ResultsLocal, lymph node, and pelvic bone recurrence was observed in 13, 4 and 2 patients, respectively. PSA levels were significantly lower in patients with negative mpMRI (0.4 ng/mL [0.4]) vs. positive mpMRI (2.2 ng/mL [4.1], p = 0.003). Median planning target volume doses in patients with visible vs. non-visible recurrences were 76 Gy vs. 70 Gy. Overall, mean follow-up was 41 months (6–81). Biochemical relapse-free survival (bRFS) at 3 years was 82.3% and 82.5%, respectively, for the negative and positive mpMRI groups (p = 0.800). Three-year rates of late grade ≥2 urinary and rectal toxicity were 14.8% and 1.9%, respectively; all but one patient recovered without sequelae.ConclusionSRT to the macroscopic recurrence identified by mpMRI is a feasible and well-tolerated option. In this study, there were no differences in bRFS between MRI-positive and MRI-negative patients, indicating effective targeting of MRI-positive lesions. 相似文献
154.
Llis A. Carlos‐Júnior Matthew Spencer Danilo Mesquita Neves Timothy Peter Moulton Dbora de Oliveira Pires Clovis Barreira e Castro Carlos Renato Rezende Ventura Carlos Eduardo Leite Ferreira Cristiana Silveira Serejo Simone Oigman‐Pszczol Fernanda Araújo Casares Marcelo Checoli Mantelatto Joel Christopher Creed 《Diversity & distributions》2019,25(5):743-757
155.
156.
157.
Cecilia Soldatini Yuri V. Albores-Barajas Alejandro Ramos-Rodriguez Adrian Munguia-Vega Eduardo González-Rodríguez Carlo Catoni Giacomo Dell'Omo 《Population Ecology》2019,61(2):227-239
During the breeding season, seabird foraging trips are constrained by nest attendance schedule and are necessarily colony centred. Oceanographic cues play a major role in the choice of foraging areas to minimize the time spent away from the nest. Here, we analysed the foraging tracks of Black-vented Shearwaters Puffinus opisthomelas during the incubation and chick-rearing periods of 2016 and 2017 at Isla Natividad (Mexico). We applied expectation-maximization binary clustering to track data to clusterize different behaviour patterns during foraging flights. We then applied binary generalized linear mixed models to characterize of foraging areas based on of environmental variables. We finally used kernel estimation techniques to describe main foraging areas. In 2016, breeding shearwaters used two core areas for foraging and resting on the water; the core area delineated by males was located northward from the colony in the Vizcaino Bay and the core area for females was located southward from the colony at the entrance of San Ignacio Lagoon. In 2017, males and females used the same areas with no evident segregation. Our study provided the first information on Black-vented Shearwater foraging areas during the breeding season and indicated that sexual segregation within coastal waters off the central Baja California Peninsula might be a foraging strategy during years of warmer ocean, likely less productive regimes. Factors including ocean-climate-mediated sexual segregation at sea, leading to interannual variation in foraging areas, should be considered when evaluating management actions intended to protect critical foraging habitats for Black-vented Shearwaters. 相似文献
158.
159.
Torres MR Sousa AP Silva Filho EA Melo DF Feitosa JP de Paula RC Lima MG 《Carbohydrate research》2007,342(14):2067-2074
Alginate fractions from Sargassum vulgare brown seaweed were characterized by (1)H NMR and fluorescence spectroscopy and by rheological measurements. The alginate extraction conditions were investigated. In order to carry out the structural and physicochemical characterization, samples extracted for 1 and 5h at 60 degrees C were further purified by re-precipitation with ethanol and denoted as SVLV (S. vulgare low viscosity) and SVHV (S. vulgare high viscosity), respectively. The M/G ratio values for SVLV and SVHV were 1.56 and 1.27, respectively, higher than the ratio for most Sargassum spp. alginates (0.19-0.82). The homopolymeric blocks F(GG) and F(MM) of these fractions characterized by (1)H NMR spectroscopy were 0.43 and 0.55 for SVHV and 0.36 and 0.58 for SVLV samples, respectively, these values typically being within 0.28-0.77 and 0.07-0.41, respectively. Therefore, the alginate samples from S. vulgare are much richer in mannuronic block structures than those from other Sargassum species. Values of M(w) for alginate samples were also calculated using intrinsic viscosity data. The M(w) value for SVLV (1.94 x 10(5)g/mol) was lower than that for SVHV (3.3 x 10(5)g/mol). Newtonian behavior was observed for a solution concentration as high as 0.7% for SVLV, while for SVHV the solutions behaved as a Newtonian fluid up to 0.5%. The optimal conditions for obtaining the alginates from S. vulgare were 60 degrees C and 5h extraction. Under these conditions, a more viscous alginate in higher yield was extracted from the seaweed biomass. 相似文献
160.
Furland NE Oresti GM Antollini SS Venturino A Maldonado EN Aveldaño MI 《The Journal of biological chemistry》2007,282(25):18151-18161
Very long-chain (C24 to C34) polyunsaturated fatty acids (VLCPUFA) are important constituents of sphingomyelin (SM) and ceramide (Cer) in testicular germ cells. In the present paper we focused on the SM and Cer and their fatty acids in spermatozoa and their main regions, heads and tails. In bull and ram spermatozoa, SM was the third most abundant phospholipid and VLCPUFA were the major acyl groups ( approximately 70%) of SM and Cer. In rat epididymal spermatozoa the SM/Cer ratio was low in the absence of and could be maintained high in the presence of the cation chelator EDTA, added to the medium used for sperm isolation. This fact points to the occurrence of an active divalent cation-dependent sphingomyelinase. Bull and rat sperm had an uneven head-tail distribution of phospholipid, with virtually all the VLCPUFA-rich SM located at the head, the lower SM content in the rat being determined by the lower sperm head/tail size ratio. Most of the SM from bull sperm heads was readily solubilized with 1% Triton X-100 at 4 degrees C. The detergent-soluble SM fraction was richer in VLCPUFA than the nonsoluble fraction and richer in saturated fatty acids. Cer was produced at the expense of SM, thus decreasing severalfold the SM/Cer ratio in rat spermatozoa incubated for 2 h in presence of the sperm-capacitating agents, calcium, bicarbonate, and albumin. The generation of Cer from SM in the sperm head surface may be an early step among the biochemical and biophysical changes known to take place in the spermatozoon in the physiological events preceding fertilization. 相似文献